U.S. patent number 6,660,686 [Application Number 09/863,341] was granted by the patent office on 2003-12-09 for photocatalyst and process for producing the same.
This patent grant is currently assigned to Kabushiki Kaisha Toyota Chuo Kenkyusho. Invention is credited to Asim Bhaumik, Shinji Inagaki.
United States Patent |
6,660,686 |
Inagaki , et al. |
December 9, 2003 |
Photocatalyst and process for producing the same
Abstract
A photocatalyst comprising a porous material, wherein the porous
material comprises a compound with a basic framework having metal
atoms bonded to phosphorus atoms by way of oxygen atoms, the metal
atoms is selected from the group consisting of titanium atoms and
zirconium atoms.
Inventors: |
Inagaki; Shinji (Aichi-gun,
JP), Bhaumik; Asim (Calcutta, IN) |
Assignee: |
Kabushiki Kaisha Toyota Chuo
Kenkyusho (Aichi-gun, JP)
|
Family
ID: |
27343490 |
Appl.
No.: |
09/863,341 |
Filed: |
May 24, 2001 |
Foreign Application Priority Data
|
|
|
|
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May 24, 2000 [JP] |
|
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2000-153585 |
May 24, 2000 [JP] |
|
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2000-153599 |
Feb 6, 2001 [JP] |
|
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2001-029882 |
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Current U.S.
Class: |
502/349; 502/208;
502/350 |
Current CPC
Class: |
B01J
27/16 (20130101); B01J 27/1802 (20130101); B01J
29/82 (20130101); B01J 35/002 (20130101); B01J
35/004 (20130101); B01J 35/1061 (20130101); C01B
37/005 (20130101) |
Current International
Class: |
B01J
27/14 (20060101); B01J 27/18 (20060101); B01J
29/82 (20060101); B01J 29/00 (20060101); B01J
35/00 (20060101); C01B 37/00 (20060101); B01J
023/00 (); B01J 017/18 () |
Field of
Search: |
;502/349,350,208 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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2824073 |
February 1958 |
Rylander et al. |
4085121 |
April 1978 |
Milberger et al. |
6387844 |
May 2002 |
Fujishima et al. |
6479141 |
November 2002 |
Sanbayashi et al. |
|
Other References
Deborah J. Jones, et al., , Journal of Materials Chemistry, vol.
10, pp. 1957-1963, "High Surface Area Mesoporous Titanium
phosphate: Synthesis and Surface Acidity Determination", 2000.
.
Jose Jimenez-Jimenez, et al., Advanced Materials, vol. 10, No. 10,
pp. 812-815, "Surfactant-Assisted Synthesis of a Mesoporous Form of
Zirconium Phosphate With Acidic Properties", 1998. .
Y. Sun, et al., Journal of Materials Chemistry, vol. 10, pp.
2320-2324, "Porous Zirconium Phosphates Prepared by
Surfactant-Assisted Precipitation", 2000..
|
Primary Examiner: Nguyen; Cam N.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A photocatalyst comprising a porous material, wherein said
porous material having a median pore diameter ranging from 0.2 nm
to less than 1.5 nm comprises a compound with a basic framework
having titanium atoms bonded to phosphorus atoms by way of oxygen
atoms.
2. The photocatalyst according to claim 1, wherein said basic
framework has a composition of the following formula (1):
3. The photocatalyst according to claim 1, wherein said porous
material has a pore volume ranging from 0.05 to 0.5 ml/g.
4. The photocatalyst according to claim 1, wherein said porous
material has an ion-exchange capacity ranging from 0.01 to 10
mmol/g.
5. The photocatalyst according to claim 3, wherein said pore volume
ranges from 0.1 to 0.5 ml/g.
6. A photocatalyst comprising a porous material, wherein said
porous material having a median pore diameter ranging from 1.5 nm
to 30 nm, comprises a compound with a basic framework having
titanium atoms bonded to phosphorus atoms by way of oxygen atoms,
and further wherein the value of the total volume of pores with a
diameter in the range of .+-.40% of said median pore diameter
divided by the total pore volume ranges from 0.4 to 1.
7. The photocatalyst according to claim 6, wherein said basic
framework has a composition of the following formula (2):
8. The photocatalyst according to claim 6, wherein said basic
framework is modified with an alkyl group, and wherein said alkyl
group is bonded to said phosphorus atom.
9. The photocatalyst according to claim 6, wherein said porous
material has an ion-exchange capacity ranging from 0.01 to 10
mmol/g.
10. The photocatalyst according to claim 6, wherein the pore walls
serving as partitions between the adjacent pores are
crystalline.
11. The photocatalyst according to claim 6, wherein the pore walls
serving as partitions between the adjacent pores exhibit an X-ray
diffraction pattern with at least 2 peaks at a diffraction angle of
at least 10.degree..
12. The photocatalyst according to claim 6, wherein said porous
material has a pore volume ranging from 0.05 to 1 ml/g.
13. The photocatalyst according to claim 12, wherein said porous
material has a pore volume ranging from 0.2 to 1 ml/g.
14. A process for producing a photocatalyst of claim 6, wherein
said process includes a step of reacting a titanium-containing
compound and a phosphorus-containing compound in water in the
presence of an alkylamine and hydrofluoric acid.
15. A process for producing a photocatalyst according to claim 14,
wherein the molar ratio of said hydrofluoric acid to said
phosphorus-containing compound is from 0.3 to 1.
16. A process for producing a photocatalyst according to claim 15,
wherein said phosphorus-containing compound contains at least one
compound selected from the group consisting of alkylphosphonic
acids and alkylphosphonic acid esters.
17. A process for producing a photocatalyst of claim 6, wherein
said process includes a step of reacting a titanium-containing
compound and a phosphorus-containing compound in water in the
presence of an anionic surfactant.
18. A process for producing a photocatalyst according to claim 17,
wherein said reaction is carried out at a pH of from 1 to 6.
19. A process for producing a photocatalyst according to claim 17,
wherein said phosphorus-containing compound contains at least one
compound selected from the group consisting of alkylphosphonic
acids and alkylphosphonic acid esters.
20. A photocatalyst comprising a porous material, wherein said
porous material having a median pore diameter ranging from 0.3 nm
to 2 nm comprises a compound with a basic framework having
zirconium atoms bonded to phosphorus atoms by way of oxygen atoms,
which compound has no organic group-crosslinked structure.
21. A photocatalyst according to claim 20, wherein the value of the
total volume of pores with a diameter in the range of .+-.40% of
said median pore diameter divided by the total pore volume ranges
from 0.4 to 1.
22. The photocatalyst according to claim 20, wherein said basic
framework has a composition of the following formula (3):
23. A process for producing a photocatalyst of claim 20, wherein
said process includes a step of reacting a zirconium-containing
compound and a phosphorus-containing compound in water in the
presence of a diaminoalkane and alcohol.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photocatalyst and to a process
for producing the same.
2. Related Background Art
Methods employing photocatalysts are among the existing techniques
for achieving effective utilization of solar energy. Photocatalysts
are substances that function as catalysts activated by light
irradiation, typical known ones including homogeneous catalysts
which employ metal complexes and non-homogeneous catalysts which
employ semiconductor catalysts.
The mechanism by which a photocatalyst exhibits a catalytic effect
upon light irradiation is theorized to be as follows, for
semiconductor catalysts, Specifically, a semiconductor has a band
structure in which conduction bands and valence bands are
partitioned by forbidden bands of appropriate width, and
irradiation of light of energy exceeding the band gap causes
excitation of the valence band electrons to the conduction bands.
As a result, electron holes are produced in the valence bands and
electrons in the conduction bands, and these electron holes and
electrons induce an oxidation or reduction reaction by a mechanism
similar to electrolysis.
The band gap size and the potential of the conduction band and
valence band are important factors contributing to the catalytic
activity. In addition to these, other contributing factors include
the life and ease of movement of the generated electrons and
electron holes, as well as the charge separation, and the
overvoltage and reactivity site of the oxidation-reduction
reaction.
As photocatalysts with such functions there are known semiconductor
catalysts such as TiO.sub.2, ZnO, Ta.sub.2 O.sub.5, CdS, GaP, SiC,
K.sub.4 Nb.sub.6 O.sub.17, K.sub.2 La.sub.2 Ti.sub.3 O.sub.10,
Na.sub.2 Ti.sub.6 O.sub.13, BaTi.sub.4 O.sub.9 and K.sub.3 Ta.sub.3
Si.sub.2 O.sub.13, and it has been confirmed that hydrogen and
(oxygen are produced when these catalysts are powdered, suspended
in water and irradiated with light.
With certain types of photocatalysts, it has been confirmed that
formic acid, formaldehyde, methanol, methane and the like are
produced upon light irradiation while carbon dioxide is passed
through their aqueous suspensions. It has also been reported that
catalysts with high dispersion of the semiconductor catalyst
TiO.sub.2 exhibit activity in pores of the insulator zeolite during
the conversion reaction of carbon dioxide to hydrocarbons.
In addition to those mentioned above, titanosilicate zeolites
(TS-1, TS-2) are also known as problem which hampers their
practical implementation.
It is an object of the present invention, which has been
accomplished in light of such technical problems, to provide a
photocatalyst which can induce efficient photocatalytic reaction
even when used in a small amount and with a small light irradiation
area, and which can thereby decompose water and the like at an
adequate reaction rate. It is another object of the invention to
provide a process for producing the photocatalyst.
As a result of much diligent research aimed at achieving the
aforementioned object, the present inventors have discovered that a
photocatalytic function is exhibited by porous materials composed
of compounds with a basic framework having titanium atoms and
phosphorus atoms bonded by way of oxygen atoms and porous materials
composed of compounds with a basic framework having zirconium atoms
and phosphorus atoms bonded by way of oxygen atoms. The present
invention has been completed upon the further discovery that such
photocatalysts can be used for efficient photocatalytic reaction
even in small amounts and with a small light irradiation area, thus
allowing decomposition of water and the like at a sufficiently high
reaction rate.
In other words, the photocatalyst of the invention is a
photocatalyst comprising a porous material, materials exhibiting
catalytic activity in photocatalytic reactions. Such zeolites are
porous materials with pares (micropores) of generally 0.3-1.3 nm in
size, and it is believed that their catalytic activity is exhibited
by their moderate solid acidity. In recent years it has become
possible to) synthesize titanosilicate mesoporous materials with
larger pores mesopores) than zeolite, measuring 1.5-50 nm in size,
and such substances have also been reported to exhibit activity in
photocatalytic reactions.
Because these photocatalysts allow utilization of solar energy for
sundry chemical reactions, they are being studied for effective use
in numerous fields, such as production of hydrogen and oxygen by
decomposition of water, synthesis of hydrocarbons such as methane
and methanol from carbon dioxide and water, and purification of
harmful substances such as NO.sub.x and dioxin.
SUMMARY OF THE INVENTION
Nevertheless, these photocatalysts of the prior art have slow
reaction rates in photocatalytic reactions for decomposition of
water or fixing of carbon dioxide, and since in order to adequately
accelerate the reactions it has been necessary to use large amounts
of catalyst and accomplish light irradiation over a wide area, this
has constituted a wherein the porous material comprises a compound
with a basic framework having metal atoms bonded to phosphorus
atoms by way of oxygen atoms, the metal atoms being selected from
the group consisting of titanium atoms and zirconium atoms.
The present invention includes the first to third preferred
embodiments of the photocatalyst as described below.
First Embodiment
The first embodiment of the present invention is a photocatalyst
comprising a porous material, wherein the porous material comprises
a compound with a basic framework having titanium atoms bonded to
phosphorus atoms by way of oxygen atoms and the porous material has
a median pore diameter of from 0.2 nm to less than 1.5 nm.
It is believed that in the photocatalyst according to the first
embodiment, which has a basic framework with titanium atoms and
phosphorus atoms bonded by way of oxygen atoms, the electron holes
and electrons produced by light irradiation efficiently contribute
to the catalytic reaction so that the efficiency of the catalytic
reaction is enhanced even with a small light irradiation area.
Also, since the photocatalyst of the first embodiment has pores of
the size specified above (micropores), it is possible to greatly
increase the contact area for contact of water, for example,
thereby increasing the number of reaction sites for the
photocatalytic reaction and allowing efficient decomposition of
water even with a small photocatalyst amount.
The basic framework of the photocatalyst of the first embodiment
preferably has the composition represented by the following general
formula (1).
wherein x is a number of from 0.5 to 1.5, y is a number of from 0.5
to 1.5 and z is a number of from 3 to 6.
A photocatalyst of the first embodiment having the composition
represented by general formula (1) above exhibits improved
efficiency of light absorption and efficiency of the light
irradiation-induced charge separated electron holes and electrons
participating in the photocatalytic reaction.
According to the first embodiment, the porous material preferably
has a pore volume of from 0.05 to 0.5 ml/g. If the porous material
has a pore volume within this range, the contact area will tend to
increase for contact with water, for example, thereby increasing
the number of reaction sites for the photocatalytic reaction and
tending to increase the efficiency of the photocatalytic
reaction.
Second Embodiment
The second embodiment of the present invention is a photocatalyst
comprising a porous material wherein the porous material comprises
a compound with a basic framework having titanium atoms bonded to
phosphorus atoms by way of oxygen atoms and the porous material has
the median pore diameter of from 1.5 nm to 30 nm, further wherein
the value of the total volume of pores with a diameter in the range
of .+-.40% of the median pore diameter divided by the total pore
volume is from 0.4 to 1.
Since the photocatalyst according to the second embodiment is
composed of a compound with a basic framework having titanium atoms
and phosphorus atoms bonded by way of oxygen atoms, it is possible
to incorporate numerous titanium atoms which participate in the
catalytic reaction into the compound, to exhibit more excellent
activity as a photocatalyst. The photocatalyst of the second
embodiment also has a very high surface area due to the mesopores
described above, and since this provides numerous reaction sites,
high activity can be exhibited even with a low amount of
photocatalyst.
The mesopores allow adsorption of substances of a size that cannot
easy penetrate micropores, so that catalytic action can be
exhibited for substances that do not easily undergo photocatalytic
reaction with titanosilicate zeolites and the like. Furthermore,
since the photocatalyst of the second embodiment has highly uniform
pore diameters as explained above, it is possible to achieve a
selective catalytic effect for substances of a specific size, while
also shortening the time required for the catalytic reaction.
The photocatalyst of the second embodiment preferably has the
composition represented by the following general formula (2).
wherein m is a number of from 0.1 to 1.5 and n is a number of from
2 to 5.
When the photocatalyst of the second embodiment has a composition
represented by general formula (2), the basic framework having
titanium atoms and phosphorus atoms banded by way of oxygen atoms
efficiently acts for catalytic reaction so that the catalytic
efficiency is improved.
A photocatalyst according to the second embodiment preferably has
its basic framework modified with alkyl groups, where the alkyl
groups are bonded to the phosphorus atoms. Modifying the basic
framework with alkyl groups can render the porous material surface
and pore interiors hydrophobic, to exhibit an excellent
photocatalytic effect even for highly hydrophobic substances.
In the photocatalyst of the second embodiment, the pore walls
serving as partitions between adjacent pores are preferably
crystalline, and the pore walls serving as partitions between
adjacent pores also preferably exhibit an X-ray diffraction pattern
with at least 2 peaks at a diffraction angle of at least
10.degree.. When the pore walls exhibit this characteristic, the
alignment of the atoms of the porous material will tend to be
regular, resulting in highly regularly arranged pores and improved
activity for use as a catalyst.
In the aforementioned first and second embodiments, the porous
material preferably has an ion-exchange capacity of from 0.01 to 10
mmol/g. In a photocatalyst according to the first or second
embodiment, the bonded states of the constituent atoms (number of
bonds and coordinated structure) can vary considerably when the
titanium atoms and phosphorus atoms which have different valencies
form the basic framework by way of oxygen atoms, and the basic
framework thus becomes charged or polarized. Consequently, the
photocatalyst of the first or second embodiment will exhibit a
cationic exchange property and/or anionic exchange property.
Therefore, the ion-exchange capacity can be adjusted to within the
range specified above.
Third Embodiment
The third embodiment of the present invention is a photocatalyst
comprising a porous material, wherein the porous material comprises
a compound with a basic framework having zirconium atoms bonded to
phosphorus atoms by way of oxygen atoms, further wherein the
compound has no organic group-crosslinked structure and the porous
material has the median pore diameter of from 0.3 nm to 2 nm.
Since the photocatalyst of the third embodiment is composed of a
compound with a basic framework having zirconium atoms and
phosphorus atoms bonded by way of oxygen atoms and having no
organic group-crosslinked structure, as mentioned above, it is
possible to incorporate numerous zirconium atoms which participate
in the catalytic reaction into the porous material, to achieve
sufficiently high catalytic activity when it is employed as a
catalyst. The photocatalyst of the third embodiment also has an
adequately high surface area since its pores have a median pore
size within the above specified range, and since this provides
numerous reaction sites, sufficiently high catalytic activity can
be achieved even with a low amount of catalyst,
In the photocatalyst of the third embodiment, the value of the
total volume of pores with a diameter in the range of .+-.40% of
the median pore diameter divided by the total pore volume is
preferably from 0.4 to 1. When the pore volume satisfies this
condition, the pore sizes are highly uniform and the shape
selectivity of reaction substrates for catalytic reaction will tend
to be higher.
The basic framework preferably has a composition represented by the
following general formula (3).
wherein a is a number of from 0.1 to 10 and b is a number of from 2
to 10.
When the photocatalyst of the third embodiment has a basic
framework with a composition represented by general formula (3),
the basic framework will efficiently function for improved
catalytic efficiency in catalytic reactions.
The present invention also provides a process for producing
photocatalysts according to the aforementioned second and third
embodiments.
Specifically, a photocatalyst according to the second embodiment
may be produced by a process including a step of reacting a
titanium-containing compound and a phosphorus-containing compound
in water in the presence of an alkylamine and hydrofluoric acid, or
by a process including a step of reacting a titanium-containing
compound and a phosphorus-containing compound in water in the
presence of an anionic surfactant.
In the production process using an alkylamine, the molar ratio of
the hydrofluoric acid with respect to the phosphorus-containing
compound is preferably from 0.3 to 1. When the molar ratio of the
phosphorus-containing compound and the hydrofluoric acid is a value
within this range, the crystallinity of the resulting photocatalyst
is improved, and therefore the regularity of the pore arrangement
is increased and the photocatalytic activity will tend to be
enhanced.
In the production process using an anionic surfactant, the reaction
between the titanium-containing compound and the
phosphorus-containing compound is preferably carried out at a pH of
from 1 to 6. Conducting the reaction in this pH range will tend to
increase the regularity of the pore arrangement of the
photocatalyst, and enhance its catalytic activity.
In both of these production processes, the phosphorus-containing
compound preferably contains an alkylphosphonic acid and/or an
alkylphosphonic acid ester. When the phosphorus-containing compound
contains an alkylphosphonic acid and/or an alkylphosphonic acid
ester, the resulting photocatalyst will be modified with alkyl
groups, and since this will improve the hydrophobicity on the
porous material surface and in the pore interiors, a satisfactory
catalytic effect will be exhibited even for highly hydrophobic
substances.
Both of the aforementioned processes can introduce a P.sup.+
--X.sup.- ion pair and/or a P--OH bond onto the phosphorus atoms of
the basic framework of the porous material. When a P.sup.+
--X.sup.- ion pair is introduced, the X.sup.- ion allows ion
exchange with other anions, thereby imparting an anionic exchange
property to the porous material. When a P--OH bond is introduced,
the P--OH bond polarizes into P--O.sup.- --H.sup.+, and the H.sup.+
ion allows ion exchange with other cations, thereby imparting a
cationic exchange property to the porous material.
The process for producing a photocatalyst according to the third
embodiment includes a step of reacting a zirconium-containing
compound with a phosphorus-containing compound in water in the
presence of a diaminoalkane and alcohol. According to this process,
it is possible to efficiently and reliably obtain a photocatalyst
according to the third embodiment.
The present invention will be more fully understood from the
detailed description given hereinbelow and the accompanying
drawings, which are given by way of illustration only and are not
to be considered as limiting the present invention.
Further scope at applicability of the present invention will become
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will be
apparent to those skilled in the art from this detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the X-ray diffraction pattern for the
amine template-containing porous material obtained in Example
1.
FIG. 2 is a graph showing the X-ray diffraction pattern for the
amine template-free porous material obtained in Example 2.
FIG. 3 is a graph showing the X-ray diffraction pattern for the
amine template-containing porous material obtained in Example
3.
FIG. 4 is a graph showing the X-ray diffraction pattern for the
amine template-containing porous material obtained in Example
4.
FIG. 5 is a graph showing the x-ray diffraction pattern for the
amine template-containing porous material obtained in Example
5.
FIG. 6 is a graph showing the X-ray diffraction pattern for the
template-containing porous material obtained in Example 6.
FIG. 7 is a graph showing the X-ray diffraction pattern for the
template-free porous material obtained in Example 6.
FIG. 8 is a graph showing the X-ray diffraction pattern for the
template-containing porous material obtained in Example 9.
FIG. 9 is a graph showing the X-ray diffraction patterns for the
template-containing porous materials obtained in Examples 9, 10 and
12, and the wide-angle X-ray diffraction pattern for the
template-containing porous material obtained in Example 13.
FIG. 10 is a graph showing the X-ray diffraction pattern for the
template-removed porous material obtained in Example 14 (Bragg
angle 2.theta.=2-50.degree.).
FIG. 11 is a graph showing the X-ray diffraction pattern for the
template-removed porous material obtained in Example 14 (Bragg
angle 2.theta.=2-10.degree.).
FIG. 12 is a graph showing the infrared absorption spectrum for the
amine template-free porous material obtained in Example 2.
FIG. 13 is a graph showing the infrared absorption spectrum for the
template-containing porous material obtained in Example 6.
FIG. 14 is a graph showing the infrared absorption spectrum for the
template-containing porous material obtained in Example 10.
FIG. 15 is a graph showing the infrared absorption spectrum for the
template-free porous material obtained in Example 10.
FIG. 16 is a graph showing the infrared absorption spectrum for the
template-containing porous material obtained in Example 14.
FIGS. 17 is a graph showing the .sup.31 P MAS NMR spectrum for the
amine template-containing porous material obtained in Example
4.
FIG. 18 is a graph showing the .sup.31 P MAS NMR spectrum for the
amine template-containing porous material obtained in Example
5.
FIG. 19 is a graph showing the .sup.31 P MAS NMR spectrum for the
template-containing porous material obtained in Example 6.
FIG. 20 is a graph showing the .sup.31 P MAS NMR spectrum for the
template-containing porous material obtained in Example 7.
FIG. 21 is a graph showing the .sup.31 P MAS NMR spectrum for the
template-containing porous material obtained in Example 9.
FIG. 22 is a graph showing the .sup.31 P MAS NMR spectra for the
template-containing porous material and template-removed porous
material obtained in Example 14.
FIG. 23 is a graph showing an adsorption isotherm for the
template-free porous material obtained in Example 7.
FIG. 24 is a graph showing an adsorption isotherm for the
template-free porous material obtained in Example 8.
FIG. 25 is a graph showing an adsorption isotherm for the
template-free porous material obtained in Example 9.
FIG. 26 is a graph showing an adsorption isotherm and pore
distribution curve for the template-free porous materials obtained
in Examples 9 and 12.
FIG. 27 is a graph showing an adsorption isotherm for the
template-removed porous material obtained in Example 14.
FIG. 28 is a graph showing a pore distribution curve for the
template-removed porous material obtained in Example 14.
FIG. 29 is a graph showing an adsorption isotherm for the amine
template-free porous material obtained in Example 2.
FIG. 30 is a graph showing an adsorption isotherm for the amine
template-free porous material obtained in Example 4.
FIG. 31 is a scanning electron micrograph of the amine
template-containing porous material obtained in Example 1.
FIG. 32 is a scanning electron micrograph of the amine
template-containing porous material obtained in Example 4.
FIG. 33 is a scanning electron micrograph (50,000.times.) of the
template-containing porous material obtained in Example 6.
FIG. 34 is a scanning electron micrograph (25,000.times.) of the
template-containing porous material obtained in Example 6.
FIG. 35 is a scanning electron micrograph of the
template-containing porous material obtained in Example 13.
FIG. 36 is a scanning electron micrograph of the
template-containing porous material obtained in Example 14.
FIG. 37 is a transmission electron micrograph of the
template-containing porous material obtained in Example 6.
FIG. 38 is a transmission electron micrograph of the
template-containing porous material obtained in Example 9.
FIG. 39 is a graph showing the .sup.13 C MAS NMR spectrum for the
amine template-containing porous material obtained in Example
5.
FIG. 40 is a graph showing the ultraviolet/visible light spectrum
for the amine template-free porous material obtained in Example
2.
FIG. 41 is a graph showing the ultraviolet/visible light spectrum
for the template-free porous material obtained in Example 6.
FIG. 42 is a graph showing the ultraviolet/visible light spectrum
for the template-free porous material obtained in Example 7.
FIG. 43 is an illustration of the proposed reaction pathway for
synthesis of a photocatalyst of the invention from a
titanium-containing compound and a phosphorus-containing
compound.
FIG. 44 is a reaction pathway diagram showing the proposed reaction
mechanism for synthesis of a porous material of the invention from
a zirconium-containing compound and a phosphorus-containing
compound.
FIG. 45 is a graph showing the relationship between light
irradiation time and amount of hydrogen generation for
decomposition of water by irradiation of light on the amine
template-free porous material obtained in Example 3.
FIG. 46 is a graph showing the relationship between light
irradiation time and amount of hydrogen generation for
decomposition of water by irradiation of light on the
template-removed porous material obtained in Example 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The photocatalyst of the invention is a photocatalyst comprising a
porous material, wherein the porous material is composed of a
compound having either of the following basic frameworks.
(I) A basic framework with titanium atoms and phosphorus atoms
bonded by way of oxygen atoms.
(II) A basic framework with zirconium atoms and phosphorus atoms
bonded by way of oxygen atoms.
In the photocatalyst of the invention, the following preferred
first to third embodiments may be mentioned. These embodiments will
be described in detail below.
First, the first and second embodiments will be explained.
A photocatalyst according to the first or second embodiment of the
invention has --[Ti--O--P--O].sub.n -- bonds in the molecule. Here,
n is an integer of one or greater representing the number of
repeats. According to the first embodiment of the invention, the
titanium atoms and phosphorus atoms can each form a 4-coordinated
structure or 6-coordinated structure. When a 4-coordinated
structure is formed, three-dimensional bonds are formed with an
oxygen atom positioned at least at one of the four apices of the
tetrahedron around each titanium atom or phosphorus atom. When a
6-coordinated structure is formed, three-dimensional bonds are
formed with an oxygen atom positioned at least at one of the six
apices of the octahedron around each titanium atom or phosphorus
atom.
The valencies of titanium and phosphorus atoms are 4 and 5,
respectively, and the valency electrons that do not contribute to
bonding with oxygen atoms forming the basic framework can bond with
other atoms or functional groups. For example, each titanium atom
can form a bond with a chlorine atom or OH group in addition to
bonding with oxygen atoms forming the basic framework. Each
phosphorus atom can also form a bond with a chlorine atom or OH
group in addition to bonding with oxygen atoms forming the basic
framework. The phosphorus atom can also form a bond with an alkyl
group, in addition to chlorine or OH. Preferred as alkyl groups to
bond with phosphorus atoms are linear or branched alkyl groups of 1
to 10 carbons.
The basic framework of the photocatalyst according to the first
embodiment of the invention, wherein titanium atoms and phosphorus
atoms are bonded to oxygen atoms, preferably has a composition
represented by the following general formula (1):
where x is a number of from 0.5 to 1.5, y is a number of from 0.5
to 1.5 and z is a number of from 3 to 6.
The proportion of titanium atoms and phosphorus atoms in general
formula (1) is preferably such that the ratio of titanium
atoms:phosphorus atoms=1:0.8-1.2, with 1:1 being more preferred.
When the proportion of titanium atoms and phosphorus atoms is
within this range, the regularity of the chemical structure at the
photocatalyst is improved, and the photocatalytic reaction can
occur more efficiently.
The basic framework of the photocatalyst according to the second
embodiment of the invention, wherein titanium atoms and phosphorus
atoms are banded to oxygen atoms, preferably has a composition
represented by the following general formula (2):
where m is a number of from 0.1 to 1.5 and n is a number of from 2
to 5.
The proportion of titanium atoms and phosphorus atoms as
represented in general formula (2) according to the invention is
preferably such that the ratio of titanium atoms:phosphorus
atoms=1:0.1-1.5. The proportion is more preferably 1:0.5-1.5, with
1:1 being even more preferred. When the proportion of titanium
atoms and phosphorus atoms is within this range, the regularity of
the chemical structure of the porous material is improved, and the
catalytic reaction of the photocatalyst can occur more
efficiently.
The photocatalyst according to the first embodiment of the
invention has a median pore diameter of at least 0.2 nm and less
than 1.5 nm, while the photocatalyst according to the second
embodiment of the invention has a median pore diameter of 1.5-30
nm.
The median pore diameter of the photocatalyst according to the
first embodiment is the value calculated by the following method.
Specifically, the porous material is immersed in water at
25.degree. C. and the adsorption is measured by the volume method,
after which the pressure of the adsorption water is gradually
increased and the adsorption of the water is measured at each
equilibrium pressure, to obtain a water adsorption isotherm. The
relative pressure at which the adsorption isotherm suddenly spikes
upward is determined, and the median pore diameter is calculated
from this value.
On the other hand, the median pore diameter of the photocatalyst
according to the second embodiment is the value calculated by the
following different method. Specifically, the porous material is
cooled to liquid nitrogen temperature (-196.degree. C.), nitrogen
gas is introduced, and the adsorption is determined by the volume
method. The pressure of the introduced nitrogen gas is then
gradually increased, and the adsorption of nitrogen gas at each
equilibrium pressure is plotted to obtain a nitrogen adsorption
isotherm, after which the pore size distribution curve is obtained
by the BHJ method (Barret-Joyner-Halenda method) from this
adsorption isotherm. The median pore diameter is the pore diameter
at the maximum peak of the pore size distribution curve.
For a photocatalyst according to the second embodiment of the
inventions the value of the total volume of pores with a diameter
in the range of .+-.40% of the median pore diameter divided by the
total pore volume is in the range of 0.4-1. Here, "the value of the
total volume of pores with a diameter in the range of .+-.40% of
the median pore diameter divided by the total pore volume is 0.4-1"
means that, for example, when the median pore diameter is 3.00 nm,
the total volume of pores within .+-.40% of 3.00 nm, i.e. in the
range of 1.80-4.20 nm, constitutes at least 40% of the total pore
volume. This means that a porous material satisfying this condition
has very highly uniform pore diameters.
The above-mentioned pore size distribution curve may be used to
determine the value of the total volume of pores with a diameter in
the range of .+-.40% of the median pore diameter divided by the
total pore volume. That is, the integral of the pore size
distribution curve between -40% and +40% of the median pore
diameter nay be divided by the integral of the entire pore size
distribution curve.
The photocatalyst according to the first embodiment of the
invention preferably has a pore volume of 0.05-0.5 ml/g. The pore
volume is more preferably 0.1-0.5 ml/g. on the other hand, the
photocatalyst according to the second embodiment of the invention
preferably has a pore volume of 0.05-1 ml/g. Its pore volume is
more preferably 0.2-1 ml/g.
According to the first and second embodiments, when the pore volume
is less than 0.05 ml/g the volume of pores in the porous material
is too low, such that when it is used as a photocatalyst for
decomposition of water there are fewer reaction sites with water,
and the catalytic activity tends to be lower. When the pore volume
exceeds 0.5 ml/g according to the first embodiment or when the pore
volume exceeds 1 ml/g according to the second embodiment, the void
portions increase excessively and tend to lower the strength of the
porous material. The pore volume can be determined from the
above-mentioned adsorption isotherm. The photocatalyst according to
the first embodiment of the invention may be a substance having
pores with a round or polygonal cross-section, or it my be a
lamellar structured substance.
Photocatalysts according to the first and second embodiments of the
invention have a basic framework wherein titanium atoms and
phosphorus atoms are banded by way of oxygen atoms, and as
explained above, the titanium atoms in this basic framework may
have a 4-coordinated structure or 6-coordinated structure, while
the phosphorus atoms may also have a 4-coordinated structure or
6-coordinated structure. Although the present inventors do not wish
to be restricted to any particularly theory, it is believed that in
the case where the titanium atoms and phosphorus atoms are both in
a 4-coordinated structure, the structure of TiXPO.sub.4 is formed
in the photocatalyst (where X is an anion much as Cl.sup.- or
OH.sup.-) whereas when the titanium atoms adopt a 4-coordinated
structure and the phosphorus atoms bond with double-bonding oxygen,
the structure of TiHPO.sub.5 formed in the photocatalyst.
Since the valencies of titanium atoms and phosphorus atoms are 4
and 5 respectively, it is thought that the phosphorus atoms in the
structure of TiXPO.sub.4 are positively charged and form ion pairs
with the negatively charged X. Thus, when the titanium atoms and
phosphorus atoms both adopt 4-coordinated structures in the
photocatalyst of the invention, an anion exchange property may be
exhibited. On the other hand, P--OH bonds are present in the
structure of TiHPO.sub.5, and these bonds polarize to P--O.sup.-
H.sup.+ so that the H.sup.+ exhibits strong solid acidity.
Consequently, when the titanium atoms adopt a 4-coordinated
structure and the phosphorus atoms bond with double-bonding oxygen
in the photocatalysts of the first and second embodiments of the
invention, a cationic exchange property may be exhibited.
When both the phosphorus atoms and titanium atoms have a
4-coordinated structure, the compound composing a photocatalyst of
the first or second embodiment has a structure represented by the
following chemical formula (i), for example. ##STR1##
In this formula, X.sup.- represents an anion, and examples of such
anions include OH.sup.- derived from the compounds used during
synthesis of the photocatalyst (for example, the surfactant and pH
adjustor) and Cl.sup.- derived from the compounds left during the
synthesis (for example, hydrogen chloride left after the reaction
between titanium tetrachloride and phosphoric acid).
When a photocatalyst with the structure represented by chemical
formula (i) above is contacted with a solution containing anions,
the solution penetrates the pores of the porous material and the
anion X.sup.- undergoes ion exchange with the anions in the
solution, so that the photocatalyst with the structure represented
by chemical formula (i) exhibits an anion exchange property, Here,
the ion-exchange capacity is preferably 0.01-10 mmol/g.
On the other hand, when the phosphorus atoms bond with
double-bonding oxygen and the titanium atoms have a 4-coordinated
structure, the compound composing a photocatalyst of the first or
second embodiment has a structure represented by the following
chemical formula (ii), for example. ##STR2##
This chemical formula (ii) is neutral overall, but the --OH groups
bonded to phosphorus as mentioned above polarize into --O.sup.-
H.sup.+. Consequently, when a photocatalyst with the structure
represented by chemical formula (ii) above is contacted with a
solution containing cations, the solution penetrates the pores of
the photocatalyst and the cation H.sup.+ undergoes ion exchange
with the cations in the solution, so that the photocatalyst with
the structure represented by chemical formula (ii) exhibits a
cation exchange property. Here, the ion-exchange capacity is
preferably 0.01-10 mmol/g.
The porous material of the invention can be confirmed to have the
structure of chemical formula (i) and/or chemical formula (ii) by
any of various analysis methods, For example, it is possible to
verify production of P--O--Ti bonds by the infrared absorption
spectrum, and it is possible to verify the 4-coordinated structure
or 6-coordinated structure of titanium atoms by the
ultraviolet/visible absorption spectrum. Also it is possible to
confirm the 4-coordinated structure or 6-coordinated structure
adopted by phosphorus atoms by the .sup.31 P MAS NMR spectrum.
The photocatalyst according to the second embodiment of the
invention is a porous material composed of a compound with the
structure described above, wherein the pore walls serving as
partitions between adjacent pores are preferably crystalline. Here,
crystalline pore walls means that all or a portion of the pore
walls are crystalline. The crystallinity of the pore walls can be
judged, for example, by performing powder X-ray diffraction of the
porous material and determining whether the resulting X-ray
diffraction pattern has at least 2 peaks at a diffraction angle of
at least 10.degree.. Porous materials with mesopores and with
crystalline pore walls are known among porous materials composed of
metal oxides, but no reports exist to date of porous materials with
crystalline pore walls, having a basic framework composed of
titanium atoms, phosphorus atoms and oxygen atoms, as according to
the present invention.
The process for producing the photocatalyst according to the first
embodiment of the invention is not particularly restricted. For
example, phosphoric acid (H.sub.3 PO.sub.4) may be dissolved in
deionized water, and then titanium tetrachloride (TiCl.sub.4) or a
titanium alkoxide such as titanium tetraisopropoxide added thereto
and the mixture stirred at, for example, room temperature for from
20-30 minutes to a few hours. Here, the ratio of moles of
phosphorus atoms to moles of titanium atoms is preferably about
1:1. After completion of the stirring, the mixture may be heated at
25-200.degree. C. in an autoclave for from 20-30 minutes to a few
hours to bring to completion the reaction between the phosphoric
acid and titanium tetrachloride or between the phosphoric acid and
titanium alkoxide. This yields a photocatalyst according to the
first embodiment of the invention.
When the phosphoric acid in deionized water is reacted with the
titanium tetrachloride or titanium alkoxide, a suitable amount of
hydrofluoric acid may also be added. Addition of hydrofluoric acid
can improve the crystallinity of the resulting porous material.
After reacting the phosphoric acid in deionized water with the
titanium tetrachloride or titanium alkoxide, a diaminoalkane such
as ethylenediamine, 1,6-diaminohexane or 1,12-diaminododecane may
be added as an amine template, or an acid or base may be added to
adjust the pH to, for example, between 2 and 2.8.
According to the invention, the diaminoalkane used as an amine
template preferably has a carbon number of 1-12. Addition of the
amine template can control the crystallinity and pore size of the
porous material. Also, adjustment of the pH to within the range
mentioned above can yield a porous material with satisfactory
crystallinity.
When an amine template is used, the reaction product may be heated
for firing at 300-1000.degree. C. and preferably 400-700.degree. C.
to remove the amine template. The heating time may be approximately
30 minutes, but heating is preferably carried out for an hour or
longer for complete removal of the amine template. The firing may
be conducted in air, but because a large amount of combustible gas
is generated, it is preferably conducted with introduction of an
inert gas such as nitrogen.
The amine template alternatively may be extracted with a good
solvent for the amine template. In addition, ethanol containing a
small amount of hydrochloric acid may be added and the mixture
stirred while heating at 50-70.degree. C. to extract the amine
template.
The process for producing the photocatalyst according to the second
embodiment of the invention is likewise not restricted in any
particular way. For example, it may be produced by a production
process including a step in which a titanium-containing compound
and a phosphorus-containing compound are reacted in water in the
presence of an alkylamine and hydrofluoric acid.
Here, the titanium-containing compound is not particularly
restricted so long as it can react with the phosphorus-containing
compound to fore a basic framework in which the titanium atoms and
phosphorus atoms are bonded by way of oxygen atoms, and as examples
there may be mentioned titanium tetrachloride (TiCl.sub.4) and
titanium alkoxides such as titanium tetraisopropoxde. The
titanium-containing compound may consist of only one of the
aforementioned compounds, or it may comprise two or Lore different
ones. However, it must include at least one of the aforementioned
compounds.
The phosphorus-containing compound is not particularly restricted
so long as it can react with titanium atoms to form a basic
framework in which the titanium atoms and phosphorus atoms are
bonded by way of oxygen atoms, and as examples there may be
mentioned phosphoric acid and phosphoric acid esters. The
phosphorus-containing compound may consist of only one of the
aforementioned compounds, or it may comprise two or more different
ones. However, it must include at least one of the aforementioned
compounds, and for example, it may further contain an
alkylphosphonic acid and/or an alkylphosphonic acid ester. The
alkyl group of the alkylphosphonic acid or alkylphosphonic acid
ester may be linear or branched, and preferably has a carbon number
of 1-10.
When the phosphorus-containing compound includes an alkylphosphonic
acid and/or alkylphosphonic acid ester in addition to phosphoric
acid or a phosphoric acid ester, the basic framework of the
resulting photocatalyst will be modified by the alkyl groups bonded
to the phosphorus atoms, and this will tend to increase the
hydrophobicity of the photocatalyst. When an alkylphosphonic acid
and/or alkylphosphonic acid ester is used in addition to phosphoric
acid or a phosphoric acid ester as the phosphorus-containing
compound according to the invention, the number of moles of
phosphorus atoms derived from the alkylphosphonic acid and/or
alkylphosphonic acid ester is preferably no greater than 50% of the
total moles of phosphorus atoms in the phosphorus-containing
compound.
The alkylamine used for the aforementioned production process is
not particularly restricted, and any primary, secondary or tertiary
amine including an alkyl group may be used. According to the
invention, N,N-dimethylalkylamines are preferably used as
alkylamines. Examples of preferred N,N-dimethylalkylamines are
N,N-dimethylalkylamines with alkyl groups of 8-22 carbon atoms,
such as N,N-dimlethyldecylamine, N,N-dimethyldodecylamine,
N,N-dimethyltetradecylamine and N,N-dimethyloctadecylamine.
According to the aforementioned production process, hydrofluoric
acid may be used for the reaction between the titanium-containing
compound and phosphorus-containing compound in water in the
presence of the alkylamine, in order to improve the crystallinity
of the resulting photocatalyst. In this case, the molar ratio of
hydrofluoric acid with respect to the phosphorus-containing
compound is preferably 0.3-1, and more preferably 0.5-1.
There are no particular restrictions on the reaction temperature
for the production process, and it may be conducted at room
temperature or under heating. When the reaction is carried out at
room temperature, stirring is preferably continued for about one
hour to 3 days. When heating is employed, it is preferred to use an
autoclave or the like for hydrothermal synthesis at 40-150.degree.
C. for one hour to 3 days.
In this production process, ammonia water or aqueous sodium
hydroxide may be added to adjust the pH to 2-6, and then the
reaction mixture stirred at room temperature and subjected to
hydrothermal synthesis in an autoclave. When the pH is adjusted in
this manner, the resulting photocatalyst will be composed of a
porous material with higher crystallinity.
The photocatalyst production process according to the second
embodiment of the invention may also include a step of removing the
alkylamine remaining in the pores of the porous material, after
completing the step of reacting the titanium-containing compound
and phosphorus-containing compound in water in the presence of an
alkylamine and hydrofluoric acid.
The method of removing the alkylamine may be, for example, a method
by firing or a method of treatment with a solvent such as water or
alcohol. In a method by firing, the porous material is heated at
300-1000.degree. C., and preferably 400-700.degree. C. The heating
time may be approximately 30 minutes, but the heating is preferably
continued for an hour or longer for complete removal of the
surfactant component. The firing may be conducted in air, but
because a large amount of combustible gas is generated, it is
preferably conducted with introduction of an inert gas such as
nitrogen. When a solvent is used for removal of the alkylamine from
the porous material, it is preferred to use a solvent with high
solubility for the alkylamine.
The photocatalyst according to the second embodiment of the
invention may alternatively be produced by a process including a
step of reacting the titanium-containing compound and
phosphorus-containing compound in water in the presence of an
anionic surfactant.
Here, the titanium-containing compound and phosphorus-containing
compound which are used may be the same ones as mentioned above.
The titanium-containing compound and phosphorus-containing compound
may be each of one type or combinations of two or more types. As
also explained above, the phosphorus-containing compound may
farther include an alkylphosphonic acid and/or alkylphosphonic acid
ester. The alkyl group of the alkylphosphonic acid and/or
alkylphosphonic acid ester may be linear or branched, and
preferably has 1-10 carbon atoms.
When the phosphorus-containing compound includes an alkylphosphonic
acid and/or alkylphosphonic acid ester in addition to phosphoric
acid or a phosphoric acid ester, the basic framework of the
resulting photocatalyst will be modified by the alkyl groups bonded
to the phosphorus atoms, and this will tend to increase the
hydrophobicity of the photocatalyst. When an alkylphosphonic acid
and/or alkylphosphonic acid ester is used in addition to phosphoric
acid or a phosphoric acid ester as the phosphorus-containing
compound according to the invention, the number of moles of
phosphorus atoms derived from the alkylphosphonic acid and/or
alkylphosphonic acid ester is preferably no greater than 50% of the
total moles of phosphorus atoms in the phosphorus-containing
compound.
The anionic surfactant used for this production process is not
particularly restricted, and any one with a hydrophilic group and
lipophilic group which produces an anion in water may be used; as
examples there may be mentioned sodium dodecyl sulfate,
dodecyl-p-benzenesulfonic acid, alkylphosphoric acid salts and
fatty acids. The anionic surfactant is used as a template for the
purpose of forming pores in the porous material, or for the purpose
of controlling the pore size.
There are no particular restrictions on the reaction temperature
for this production process, and it may be conducted at room
temperature or under heating. When the reaction is carried out at
room temperature, stirring is preferably continued for about one
hour to 3 days. When heating is employed, it is preferred to use an
autoclave or the like for hydrothermal synthesis at 40-150.degree.
C. for one hour to 3 days. In this production process, ammonia
water or aqueous sodium hydroxide is preferably added to adjust the
pH to 1-6, and then the reaction mixture stirred at room
temperature and subjected to hydrothermal synthesis in an
autoclave. The pH is preferably adjusted to 3-5. When the pH is
adjusted in this manner the resulting photocatalyst will be
composed of a porous material with higher crystallinity. When a
titanium alkoxide is used as the titanium-containing compound, a
step of removing the alkoxide-derived alcohol may be added.
The production process for a photocatalyst according to the second
embodiment of the invention may also include a step of removing the
anionic surfactant present in the pores of the porous material,
after completing the step of reacting the titanium-containing
compound and phosphorus-containing compound in water in the
presence of the anionic surfactant.
The method of removing the anionic surfactant may be, for example,
a method by firing or a method of treatment with a solvent such as
water or alcohol. Firing may be accomplished in the manner
described above. When a solvent is used for removal, the porous
material may be dispersed in ethanol containing ammonia water or
aqueous sodium hydroxide, for example, and the dispersion stirred
while heating at 50-70.degree. C.
In both of the production processes described above the ratio of
the total number of moles of phosphorus atoms in the
phosphorus-containing compound with respect to the total number of
moles of titanium atoms in the titanium-containing compound is
preferably 0.1-1.5, and more preferably 0.5-1.5. When the
titanium-containing compound and phosphorus-containing compound are
reacted in water, their concentration in the water is not
particularly restricted but is preferably 0.1-20 mole percent as
the total for the titanium-containing compound and
phosphorus-containing compound. The number of moles of the
alkylamine and anionic surfactant is preferably 0.1-20 mole percent
with respect to the total number of moles of the
titanium-containing compound and phosphorus-containing
compound.
A photocatalyst according to the third embodiment of the invention
will now be explained.
The photocatalyst according to the third embodiment of the
invention is composed of a compound having a framework with
zirconium atoms and phosphorus atoms bonded by way of oxygen atoms
and having no organic group-crosslinked structure; such compounds
have in the molecule bonds represented by --[Zr--O--P--O].sub.n --
(where n is an integer of 1 or greater representing the number of
repeats). Because the photocatalyst according to the third
embodiment of the invention is composed of a compound having this
kind of basic framework, the zirconium atoms can be incorporated
into the compound in an sufficiently high amount as active sites of
the catalyst without impairing the porous structure of the porous
material, so that adequately high catalytic activity can be
achieved.
The mechanism for expression of the catalytically active sites in
the photocatalyst according to the third embodiment of the
invention is conjectured by the present inventors to be as follows.
That is, it is believed that by forming the aforementioned basic
framework in the molecule, a band structure is formed in which
conduction bands and valence bands are partitioned by appropriate
forbidden bands. When heat or light energy is applied to the
compound having this band structure, the valence band electrons are
excited to the conduction bands by energy absorption, and the
electron holes of the valence bands and the electrons of the
conduction bands each act as activity centers for
oxidation-reduction reaction.
In the photocatalyst according to the third embodiment of the
invention, the zirconium atoms and phosphorus atoms can each form a
4-coordinated structure or 6-coordinated structure. When a
4-coordinated structure is formed, three-dimensional bonds are
formed with an oxygen atom positioned at least at one of the four
apices of the tetrahedron around each zirconium atom or phosphorus
atom. When a 6-coordinated structure is formed, three-dimensional
bonds are formed with an oxygen atom positioned at least at one of
the six apices of the octahedron around each zirconium atom or
phosphorus atom.
The valencies of zirconium and phosphorus atoms are 4 and 5,
respectively, and the valency electrons that do not contribute to
banding with oxygen atoms forming the basic framework can bond with
other atoms or functional groups. For example, each zirconium atom
can form a bond with a chlorine atom or hydroxyl group in addition
to bonding with oxygen atoms forming the basic framework. Each
phosphorus atom can also form a bond with a chlorine atom, hydroxyl
group or alkyl group in addition to bonding with oxygen atoms
forming the basic framework.
If the composition of the basic framework of the photocatalyst
according to the third embodiment of the invention is represented
by the following general formula (3):
using a and b as the ratios of phosphorus atoms and oxygen atoms,
respectively, with respect to zirconium atoms, then preferably a is
a number of from 0.1 to 10 and b a number of from 2 to 10, and sore
preferably, a is a number of from 0.7 to 1.2 and b a number of from
3 to 6.
When the proportion of phosphorus atoms and oxygen atoms with
respect to zirconium atoms satisfies this condition, the regularity
of the chemical structure of the photocatalyst is improved, and the
catalytic activity of the photocatalyst tends to be increased.
The photocatalyst according to the third embodiment of the
invention has pores with a median pore diameter of 0.3-2 nm. When
the median pore diameter of the pores is within this range, the
porous material exhibits sufficiently high adsorption for the
starting compounds in the catalytic reaction, and the starting
compounds are introduced into the pores containing the active sites
at an adequately high concentration for an enhanced reaction rate.
Since a strong potential field is formed inside the fine pores due
to buildup of Van der Waals forces from the pore walls which act
3-dimensionally, the catalytic reaction rate is also speeded by
this potential field. In addition, since the surface area of the
photocatalyst of the invention having such pores is sufficiently
large, it can provide a satisfactory large number of reaction
sites. Consequently, the photocatalyst according to the third
embodiment of the invention can adequately reduce the time and
amount of catalyst necessary for the catalytic reaction. The median
pore diameter of the photocatalyst according to the third
embodiment of the invention is the same as for the photocatalyst
according to the second embodiment.
In the photocatalyst according to the third embodiment of the
invention, the value of the total volume of pores with a diameter
in the range of .+-.40% of the median pore diameter divided by the
total pore volume is preferably 0.4-1. if the pore volume does not
satisfy this condition, the pore size uniformity will tend to be
inadequate and the shape selectivity of reaction substrates for the
catalytic reaction will tend to be lower.
The pore volume of the photocatalyst according to the third
embodiment of the invention is preferably (0.05-0.5 ml/g and more
preferably 0.1-0.5 ml/g. If the pore volume is less than the lowest
limit of these ranges, the pore volume of the porous material may
be too low, and when the porous material is used as a photocatalyst
for decomposition of water, for example, the reaction sites will
tend to be reduced, thereby lowering the catalytic activity. On the
other hand, if the pore volume exceeds the highest limit, the void
portions of the porous material increase excessively and tend to
lower the strength of the porous material. The pore volume can be
determined from the adsorption isotherm.
The photocatalyst according to the third embodiment of the
invention has a basic framework wherein zirconium atoms and
phosphorus atoms are bonded by way of oxygen atoms, and as
explained above, the zirconium atoms in this basic framework may
have a 4-coordinated structure or 6-coordinated structure, while
the phosphorus atoms may also have a 4-coordinated structure or
6-coordinated structure. Although the present inventors do not wish
to be restricted to any particularly theory, it is relieved that in
the case where the zirconium atoms and phosphorus atoms are both in
a 4-coordinated structure, the structure of ZrXPO.sub.4 is formed
in the porous material (where X is an anion such as Cl.sup.- or
OH.sup.-), whereas when the zirconium atoms adopt a 4-coordinated
structure and the phosphorus atoms bond with double-bonding oxygen,
the structure of ZrHPO.sub.4 is formed in the porous material.
Since the valencies of zirconium atoms and phosphorus atoms are 4
and 5 respectively, it is thought that the phosphorus atoms in the
structure of ZrXPO.sub.4 are positively charged and form ion pairs
with the negatively charged X. Thus, when the zirconium atoms and
phosphorus atoms both adopt 4-coordinated structures in the
photocatalyst of the inventions an anion exchange property may be
exhibited. In this case, the photocatalyst of the third embodiment
has a structure represented by the following formula (iii).
##STR3##
In formula (iii), the anion represented by X.sup.- may be, for
example, an anion such as OH.sup.- derived from the compounds used
during synthesis of the photocatalyst (for example, the surfactant
and pH adjustor) or an anion such as Cl.sup.- derived from the
compounds left during the synthesis (for example, hydrogen chloride
left after the reaction between zirconium tetrachloride and
phosphoric acid).
When a photocatalyst comprising a porous material with the
structure represented by formula (iii) above is contacted with a
solution containing anions, the solution penetrates the pores of
the photocatalyst and ion exchange occurs between X and the anions
in the solution, so that an anion exchange property is exhibited.
Here, the ion-exchange capacity is preferably 0.01-10 mmol/g.
On the other hand, P--OH bonds are present in the structure of
ZrHPO.sub.4, and these bonds polarize to P--O.sup.- H.sup.+ so that
the H.sup.+ exhibits strong solid acidity. Thus, it is thought that
the photocatalyst of the third embodiment exhibits a cationic
exchange property when the zirconium atoms have a 4-coordinated
structure and the phosphorus atoms bond with double-bonding oxygen.
In this case, the photocatalyst of the third embodiment has a
structure represented by the following formula (iv). ##STR4##
This formula (iv) is neutral overall, but since the hydroxyl groups
bonded to phosphorus atoms can polarize into P--O.sup.- H.sup.+ as
explained above, when a porous material with the structure
represented by formula (iv) above is contacted with a solution
containing cations, the solution penetrates the pores of the porous
material and H.sup.+ undergoes ion exchange with the cations in the
solution, so that a cation exchange property is exhibited. Here,
the ion-exchange capacity is preferably 0.01-10 mmol/g. The porous
material of the invention can be confirmed to have the structure
represented by formula (iii) or formula (iv) by the same publicly
known analysis methods mentioned above.
A photocatalyst according to the third embodiment of the invention
having such a structure can be efficiently and reliably obtained by
the production process described below. Specifically, the
production process for a photocatalyst according to the third
embodiment is characterized by including a step of reacting a
zirconium-containing compound and a phosphorus-containing compound
in water in the presence of a diaminoalkane and alcohol.
There are no particular restrictions on the zirconium-containing
compounds to be used in the production process for a photocatalyst
according to the third embodiment so long as they can react with
phosphorus-containing compounds to form a basic framework in which
the zirconium atoms and phosphorus atoms are bonded by way of
oxygen atoms; specifically, however, there may be mentioned
zirconium tetrachloride (ZrCl.sub.4), zirconium alkoxides such as
zirconium tetraisopropoxide (Zr(OiPr).sub.4), zirconium
actetylacetonate and sulfated zirconia. These zirconium-containing
compounds my be used alone or in combinations of two or more.
The phosphorus-containing compound is not particularly restricted
so long as it can react with the zirconium-containing compound to
form a basic framework in which the zirconium atoms and phosphorus
atoms are bonded by way of oxygen atoms, and as specific examples
there may be mentioned phosphoric acid (H.sub.3 PO.sub.4) and
phosphoric acid esters. These phosphorus-containing compounds may
be used alone or in combinations of two or more. The
phosphorus-containing compound may further contain an
alkylphosphonic acid and/or an alkylphosphonic acid ester in
addition to these compounds. The alkyl group of the alkylphosphonic
acid or alkylphosphonic acid ester may be linear or branched, and
preferably has a carbon number of 1-10.
When the phosphorus-containing compound includes an alkylphosphonic
acid and/or alkylphosphonic acid ester in addition to phosphoric
acid or a phosphoric acid ester, the basic framework of the
resulting photocatalyst will be modified by the alkyl groups bonded
to the phosphorus atoms, and this will tend to increase the
hydrophobicity of the photocatalyst. The proportion of phosphorus
atoms derived from the alkylphosphonic acid and/or alkylphosphonic
acid ester is preferably no greater than 50% in terms of moles with
respect to the total moles of phosphorus atoms in the
phosphorus-containing compound.
The amount of zirconium-containing compound and
phosphorus-containing compound used is appropriately selected based
on the composition of the basic framework of the intended
photocatalyst, but the ratio of the total moles of phosphorus atoms
in the phosphorus-containing compound with respect to the total
moles zirconium atoms in the zirconium-containing compound is
preferably 0.1-10, and more preferably 0.7-1.2. The concentration
of these compounds in water is not particularly restricted, but is
preferably 0.1-20 mole percent as the total for the
zirconium-containing compound and phosphorus-containing
compound.
In the production process for a photocatalyst according to the
third embodiment, a diaminoalkane is used as the template. As
specific diaminoalkanes there may be mentioned
1,12-diaminododecane, 1,10-diaminodecane, 1,8-diaminooctane and
1,6-diaminohexane. Of these, diaminoalkanes with alkyl groups of
8-14 carbon atoms are preferred. The amount of diaminoalkane used
is preferably 0.1-20 mole percent with respect to the total moles
of the zirconium-containing compound and phosphorus-containing
compound.
In the production process for a photocatalyst according to the
third embodiment, an alcohol may be used during reaction of the
zirconium-containing compound and phosphorus-containing compound in
water in the presence of the diaminoalkane, in order to improve the
crystallinity of the resulting porous material. As specific
alcohols there may be mentioned methanol, ethanol, n-propanol and
i-propanol. These alcohols may be used alone or in combinations of
two or more. The amount of alcohol used is preferably 0.3-1 mole
and more preferably 0.5-1 mole to 1 mole of the
phosphorus-containing compound.
There are no particular restrictions on the reaction temperature
for the production process for a photocatalyst according to the
third embodiment, and it may be conducted at room temperature or
under heating. When the reaction temperature is room temperature,
the reaction solution is preferably subjected to the reaction for
about one hour to 3 days while stirring. When heating is employed,
it is preferred to use an autoclave or the like for hydrothermal
synthesis at 40-1.50.degree. C. for one hour to 3 days.
In the production process for a photocatalyst according to the
third embodiment, ammonia water or aqueous sodium hydroxide may be
used to adjust the pH to 2-6. Adjusting the pH of the reaction
solution to within this range tends to give a photocatalyst
composed of a porous material with higher crystallinity.
The photocatalyst production process according to the third
embodiment may also include a step of removing the diaminoalkane
remaining in the pores of the porous material, after completing the
step of reacting the zirconium-containing compound and
phosphorus-containing compound in water in the presence of the
diaminoalkane and alcohol. The method of removing the diaminoalkane
is the same as for a photocatalyst according to the first
embodiment.
As explained above, photocatalysts according to the invention
having the composition and chemical structure described above thus
produce efficient photocatalytic reaction even when used in low
amounts and with a small light irradiation area. As particularly
preferred uses, the photocatalysts may be employed as
photocatalysts for production of hydrogen by photodecomposition of
water, photosynthesis of hydrocarbons (such as methane and
methanol) from carbon dioxide and water (carbon dioxide fixation)
and photopurification of NO.sub.x, as antifouling construction
materials, antimicrobial materials, superhydrophilic materials,
superhydrophobic materials and deodorizing materials, as catalysts
for photodecomposition of dioxin and environmental hormones, as
freshness retaining materials based on ethylene decomposition, as
water treatment materials (for removal of E. coli, organic chlorine
compounds, agricultural chemicals, phenols, etc.), as metal oxide
semiconductors for pigment sensitized solar cells, and as organic
compound liquid phase oxidizing catalysts.
EXAMPLES
Preferred examples of the present invention will now be explained
in detail, with the understanding that the invention is in no way
limited to these examples.
Photocatalyst of First Embodiment
Example 1
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 8.4 g
of hydrofluoric acid (HF) to 120 g of deionized water, the mixture
was vigorously stirred at room temperature. To this stirred aqueous
solution there was added dropwise 18.9 g of titanium tetrachloride
(TiCl.sub.4), and stirring was continued at room temperature for
one hour. Next, 3.0 g of ethylenediamine (H.sub.2 N--C.sub.2
H.sub.4 --NH.sub.2) was added as an amine template, and stirring
was continued at room temperature for one hour to obtain a gel-like
substance. The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:TiCl.sub.4 :HF:R:H.sub.2 O=1:1:1:0.5:66.6
Here, R represents the amine template (H.sub.2 N--C.sub.2 H.sub.4
--NH.sub.2).
The obtained gel-like substance was heated in an autoclave at
170.degree. C. (443K) for 24 hours. The heated product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hours to obtain an amine template-containing porous material.
The amine template-containing porous material was then poured into
a mixed solution of 2 g of dilute hydrochloric acid (2 mol %) and
80 ml of ethanol and the mixture was stirred at 60.degree. C.
(333K) for 6 hours to remove the ethylenediamine from the pores,
after which it was dried at room temperature to obtain an amine
template-free porous material.
Example 2
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 8.4 g
of hydrofluoric acid (HF) to 120 g of deionized water, the mixture
was vigorously stirred at room temperature. To this stirred aqueous
solution there was added dropwise 18.9 g of titanium tetrachloride
(TiCl.sub.4), and stirring was continued at room temperature for
one hour to obtain a gel-like substance. The molar ratio of the
constituent components of the resulting gel-like substance was as
follows. H.sub.3 PO.sub.4 :TiCl.sub.4 :HF:H.sub.2 O=1:1:1:66.6
The obtained gel-like substance was heated in an autoclave at
80.degree. C. (353K) for 72 hours. The heated product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hours to obtain an amine template-free porous material.
Example 3
An 11.5 g portion of phosphoric acid (H.sub.3 PO.sub.4) was
dissolved in 120 g of deionized water. While stirring this aqueous
solution, 18.9 g of titanium tetrachloride (TiCl.sub.4) was added
dropwise thereto. Stirring was continued at room temperature for
one hour. Next, 6.3 g of 1,6-diaminohexane (H.sub.2 N--C.sub.6
H.sub.12 --NH.sub.2) was added as an amine template, a 2 N aqueous
sodium hydroxide solution was added to adjust the pH to 2-2.8 and
stirring was continued at room temperature for one hour to obtain a
gel-like substance. The molar ratio of the constituent components
of the resulting gel-like substance was as follows. H.sub.3
PO.sub.4 :TiCl.sub.4 :R:NaOH:H.sub.2 O=1:1:0.5:(2.5-3.0):66.6
Here, R represents the amine template (H.sub.2 N--C.sub.6 H.sub.12
--NH.sub.2).
The obtained gel-like substance was heated in an autoclave at
170.degree. C. (443K) for 48 hours. The heated product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hears to obtain an amine template-containing porous material.
The amine template-containing porous material was then poured into
a mixed solution of 2 g of dilute hydrochloric acid (2 mol %) and
80 ml of ethanol and the mixture was stirred at 60.degree. C.
(333K) for 6 hours to remove the 1,6-diaminohexane from the pores,
after which it was dried at room temperature to obtain an amine
template-free porous material.
Example 4
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 8.4 g
of hydrofluoric acid (HF) to 120 g of deionized water, the mixture
was vigorously stirred at room temperature. To this stirred aqueous
solution there was added dropwise 18.9 g of titanium tetrachloride
(TiCl.sub.4), and stirring was continued at room temperature for
one hour. Next, 9.45 g of 1,6-diaminohexane (H.sub.2 N--C.sub.6
H.sub.12 --NH.sub.2) was added as an amine template, and stirring
was continued at room temperature for one hour to obtain a gel-like
substance. The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:TiCl.sub.4 :HF:R:H.sub.2 O=1:1:1:0.75:66.6
Here, R represents the amine template (H.sub.2 N--C.sub.6 H.sub.12
--NH.sub.2).
The obtained gel-like substance was heated in an autoclave at
170.degree. C. (443K) for 24 hours. The heated product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hours to obtain an amine template-containing porous material.
The amine template-containing porous material was then poured into
a mixed solution of 2 g of dilute hydrochloric acid (2 mol %) and
80 ml of ethanol and the mixture was stirred at 60.degree. C.
(333K) for 6 hours to remove the 1,6-diaminohexane from the pores,
after which it was dried at room temperature to obtain an amine
template-free porous material.
Example 5
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 8.4 g
of hydrofluoric acid (HF) to 120 g of deionized water, the mixture
was vigorously stirred at room temperature. To this stirred aqueous
solution there was added dropwise 18.9 g of titanium tetrachloride
(TiCl.sub.4), and stirring was continued at room temperature for
one hour. Next, 5 g of 1,12-diaminododecane (H.sub.2 N--C.sub.12
H.sub.24 --NH.sub.2) was added as an amine template, and stirring
was continued at room temperature for one hour to obtain a gel-like
substance. The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:TiCl.sub.4 :HF:R:H.sub.2 O=1:1:1:0.25:66.6
Here, R represents the amine template (H.sub.2 N--C.sub.12 H.sub.24
--NH.sub.2).
The obtained gel-like substance was heated in an autoclave at
140.degree. C. (413K) for 72 hours. The heated product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hours to obtain an amine template-containing porous material.
The amine template-containing porous material was then poured into
a mixed solution of 2 g of dilute hydrochloric acid (2 mol %) and
80 ml of ethanol and the mixture was stirred at 60.degree. C.
(333K) for 6 hours to remove the 1,12-diaminododecane from the
pores, after which it was dried at room temperature to obtain an
amine template-free porous material.
Photocatalyst of Second Embodiment
Example 6
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 8.4 g
of hydrofluoric acid (HF) to 120 g of deionized water, the mixture
was vigorously stirred at room temperature. To this stirred aqueous
solution there was added dropwise 18.9 g of titanium tetrachloride
(TiCl.sub.4), and stirring was continued at room temperature for
one hour. Next, 17.5 g of N,N-dimethyltetradecylamine was added as
a template, and stirring was continued at room temperature for 3
days to obtain a gel-like substance. The molar ratio of the
constituent components of the resulting gel-like substance was as
follows. H.sub.3 PO.sub.4 :TiCl.sub.4 :HF:R:H.sub.2
O=1:1:1:0.5:66.6
Here, R represents the template (N,N-dimethyltetradecylamine).
After completion of the stirring, the obtained product was filtered
and the solid portion obtained by filtering was washed several
times with deionized water and dried at 100.degree. C. (373K) for a
few hours to obtain a template-containing porous material. The
template-containing porous material was then stirred at root
temperature for 12 hours in a mixed solution of 2 g of dilute
hydrochloric acid (2 mol %) and 80 ml of ethanol. The stirring in
the dilute hydrochloric acid and ethanol mixed solution was carried
out a total of 3 times to remove the template from the pores. The
solid portion was then removed from the dilute hydrochloric acid
and ethanol mixed solution by filtration, and heated at 105.degree.
C. (378K) for one hour to obtain a template-free porous material.
The white template-containing porous material obtained in this
example changed to light yellow by the stirring in the dilute
hydrochloric acid and ethanol mixed solution, but returned to a
white color by the heating at 105.degree. C. (378K).
Example 7
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 21.8
g of sodium dodecyl sulfate (anionic surfactant) as a template to
120 g of deionized water, the mixture was vigorously stirred at
room temperature. To this stirred aqueous solution there was added
dropwise 18.9 g of titanium tetrachloride (TiCl.sub.4), and then
ammonia water (25 wt % aqueous solution) was added for adjustment
of the pH to about 4 to obtain a gel-like substance. The molar
ratio of the constituent components of the resulting gel-like
substance was as follows. H.sub.3 PO.sub.4 :TiCl.sub.4 :R:H.sub.2
O=1:1:0.75:66.6
Here, R represents the template (sodium dodecyl sulfate).
The obtained gel-like substance was heated at 60.degree. C. (333K)
for 3 days using an autoclave, and the resulting product was
filtered. The solid portion obtained by filtering was washed
several times with deionized water and dried at room temperature,
to obtain a template-containing porous material. Next, a mixed
solution of 2 mL of ammonia water (25 wt % aqueous solution) and
150 mL of ethanol was added to 2 g of this template-containing
porous material, and the mixture was stirred at 25.degree. C.
(298K) for 6 hours to remove the template from the pores. The solid
portion was then removed from the mixed solution of ammonia water
and ethanol and dried at room temperature to obtain a template-free
porous material.
Example 8
A gel-like substance was obtained in the same manner as Example 7,
except that the weights of phosphoric acid (H.sub.3 PO.sub.4) and
sodium dodecyl sulfate used were 1.9 g and 14.4 g, respectively.
The molar ratio of the constituent components of the resulting
gel-like substance was as follows. H.sub.3 PO.sub.4 :TiCl.sub.4
:R:H.sub.2 O=1:6:0.5:66.6
Here, R represents the template (sodium dodecyl sulfate).
The gel-like substance was used to obtain a template-containing
porous material and a template-free porous material in the same
manner as Example 7.
Example 9
A gel-like substance was obtained in the same manner as Example 7,
using a mixture of 6.1 g of phosphoric acid and 6.2 g of
methylphosphonic acid diethyl ester (CH.sub.3 PO(OC.sub.2
H.sub.5).sub.2) instead of 11.5 g of phosphoric acid (H.sub.3
PO.sub.4). The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:CH.sub.3 PO(OC.sub.2 H.sub.5).sub.2 :TiCl.sub.4 :R:H.sub.2
O=0.5:0.5:1:0.75:66.6
Here, R represents the template (sodium dodecyl sulfate).
The gel-like substance was used to obtain a template-containing
porous material and a template-free porous material in the same
manner as Example 7, except that the autoclave heating was carried
out at 45.degree. C. (318K) for 2 days. These porous materials were
modified with methyl groups derived from the methylphosphonic acid
diethyl ester.
Example 10
After adding 11.5 g of phosphoric acid (H.sub.3 PO.sub.4) and 16.2
g of dodecyl-p-benzenesulfonic acid (anionic surfactant) as a
template to 120 g of deionized water, the mixture was vigorously
stirred at room temperature. To this stirred aqueous solution there
was added dropwise 18.9 g of titanium tetrachloride (TiCl.sub.4),
and then ammonia water (25 wt % aqueous solution) was added for
adjustment of the pH to about 4 to obtain a gel-like substance. The
molar ratio of the constituent components of the resulting gel-like
substance was as follows. H.sub.3 PO.sub.4 :TiCl.sub.4 :R:H.sub.2
O=1:1:0.5:66.6
Here, R represents the template (dodecyl-p-benzenesulfonic
acid).
The obtained gel-like substance was heated at 45.degree. C. (318K)
for 1 day using an autoclave, and the resulting product was
filtered. The solid portion obtained by filtering was washed
several times with deionized water and dried at room temperature,
to obtain a template-containing porous material. Next, a mixed
solution of 2 mL of ammonia water (25 wt % aqueous solution) and
150 mL of ethanol was added to 2 g of this template-containing
porous material, and the mixture was stirred at 25.degree. C.
(298K) for 6 hours to remove the template from the pores. The solid
portion was then removed from the mixed solution of ammonia water
and ethanol and dried at room temperature to obtain a template-free
porous material.
Example 11
A gel-like substance was obtained in the same manner as Example 10,
except that the weight of phosphoric acid (H.sub.3 PO.sub.4) was
2.85 g. The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:TiCl.sub.4 :R:H.sub.2 O=1:4:0.5:66.6
Here, R represents the template (dodecyl-p-benzenesnulfonic
acid).
The gel-like substance was used to obtain a template-containing
porous material and a template-free porous material in the same
manner as Example 10.
Example 12
A gel-like substance was obtained in the same manner as Example 10,
except that the weight of phosphoric acid (H.sub.3 PO.sub.4) was
1.45 g. The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:TiCl.sub.4 :R:H.sub.2 O=1:8:0.5:66.6
Here, R represents the template (dodecyl-p-benzenesulfonic
acid).
The gel-like substance was used to obtain a template-containing
porous material and a template-free porous material in the same
manner as Example 10.
Example 13
A gel-like substance was obtained in the same manner as Example 10,
using a mixture of 6.1 g of phosphoric acid and 6.2 g of
methylphosphonic acid diethyl ester (CH.sub.3 PO(OC.sub.2
H.sub.5).sub.2) instead of 11.5 g of phosphoric acid (H.sub.3
PO.sub.4). The molar ratio of the constituent components of the
resulting gel-like substance was as follows. H.sub.3 PO.sub.4
:CH.sub.3 PO(OC.sub.2 H.sub.5).sub.2 :TiCl.sub.4 :R:H.sub.2
O=0.5:0.5:1:0.5:66.6
Here, R represents the template (dodecyl-p-benzenesulfonic
acid).
The gel-like substance was used to obtain a template-containing
porous material and a template-free porous material in the same
manner as Example 10. These porous materials were Modified with
methyl groups derived from the methylphosphonic acid diethyl
ester.
Photocatalyst of Third Embodiment
Example 14
To 70 ml of a mixed solution of isopropanol and water
(isopropanol/water weight ratio: 1/1) there were added 23.4 g of
1,12-diaminododecane as a template and 11.5 g of phosphoric acid
(H.sub.3 PO.sub.4), and the mixture was vigorously stirred.
Next, 77.2 g of a mixture of zirconium tetrapropoxide
(Zr(OPr).sub.4 : Pr representing a propyl group) and isopropanol
(zirconium tetrapropoxide/isopropanol weight ratio: 1/1) was slowly
added to the above-mentioned mixture, and after further adding 170
ml of water, hydrothermal treatment was carried out at 60.degree.
C. (333K) for 1 day to obtain a gel-like substance. The molar ratio
of the constituent components of the resulting gel-like substance
was as follows. Zr(OPr).sub.4 :H.sub.3 PO.sub.4 :R:H.sub.2
O=1:1:0.25:100
Here, R represents the template (1,12-diaminododecane).
The obtained gel-like substance was filtered, and the obtained
solid portion was washed with water and dried at room temperature
to obtain a template-containing porous material. A 2 g portion of
this template-containing porous material was added to a mixed
solution of 2 g of dilute hydrochloric acid (2 mol %) and 100 ml of
ethanol, and the mixture was subjected to reflux at 40.degree. C.
(313K) for 4 hours to remove the template and obtain the target
porous material.
The porous materials (photocatalysts) obtained in Examples 1-14
were then subjected to X-ray diffraction, fluorescent X-ray
diffraction, infrared absorption measurement, .sup.31 P MAS NMR
spectroscopy, nitrogen absorption, moisture absorption, ICP
emission spectroscopy, scanning electron microscope observation,
.sup.13 C MAS NMR spectroscopy, ultraviolet/visible absorption
spectroscopy, ion-exchange capacity measurement and water
decomposition by light irradiation. The details are explained
below.
X-ray Diffraction
An RAD-B (product of Rigaku Co., X-rays: CuK.alpha. rays) was used
for powder X-ray diffraction of the amine template-containing
porous materials obtained in Examples 1 and 3-5, the amine
template-free porous material obtained in Example 2 and the porous
materials obtained in Examples 6, 9 and 10-13.
FIGS. 1-5 show the X-ray diffraction patterns for the porous
materials of Examples 1-5, respectively. FIGS. 6, 7 and 8 show the
X-ray diffraction patterns for the template-containing porous
material and template-free porous material obtained in Example 6
and the template-containing porous material obtained in Example
9.
FIG. 9 shows the x-ray diffraction pattern for the
template-containing porous material obtained in Example 9 (pattern
"a" in FIG. 9), the X-ray diffraction pattern for the
template-containing porous material obtained in Example 10 (pattern
"c" in FIG. 9) and the X-ray diffraction pattern for the
template-containing porous material obtained in Example 12 (pattern
"b" in FIG. 9).
As seen in FIGS. 1-5, it was confirmed that the produced porous
materials were crystalline on the atomic level. FIG. 6 shows peaks
at 1.910.degree., 3.210.degree., 3.730.degree. and 4.740.degree.
corresponding to the face indices (100), (110), (200) and (210),
thus demonstrating that the porous material obtained in Example 6
has a two-dimensional hexagonal pore arranged structure.
As a result of the X-ray diffraction of the template-containing
porous materials obtained in Examples 10-13, it was found that at
least 2 peaks appear in a wide-angle region (diffraction angle of
10.degree. or larger) in the X-ray diffraction patterns of Examples
10-13. A representative example is the X-ray diffraction pattern of
the wide-angle region for the template-containing porous material
of Example 13, shown in FIG. 9. The fact that at least 2 peaks
appear in a wide-angle of 10.degree. or larger in this X-ray
diffraction pattern indicates that the pore walls serving as
partitions between adjacent pores are crystalline.
Next, an RINT-2200 (product of Rigaku Co., X-rays: CuK.alpha. rays)
was used for powder X-ray diffraction of the template-containing
porous material and template-removed porous material obtained in
Example 14.
FIGS. 10 and 11 are graphs showing the X-ray diffraction patterns
for each of the template-removed porous materials, where FIG. 10 is
a diffraction pattern for the range of Bragg angle
2.theta.=2-50.degree., and FIG. 11 is a magnified view of the
2.theta.=2-10.degree. portion of FIG. 10. In these graphs, a
diffraction peak is seen in the low angle range of
2.theta.<10.degree., but no characteristic diffraction peak is
seen in the range of 2.theta.=10-50.degree., thus confirming that
the obtained porous material has only a long periodic structure and
its pore walls have an amorphous structure. The d.sub.100 of the
template-containing porous material is 2.65 nm, while the d.sub.100
of the template-removed porous material is 2.42 nm.
Fluorescent X-ray Analysis
Fluorescent X-ray analysis of the template-removed porous material
obtained in Example 14 demonstrated that the chemical composition
was Zr.sub.1 P.sub.1 O.sub.4.5.
Infrared Absorption Spectroscopy
An FT/IR-5M (JASCO Corp.) was used for measurement of the infrared
absorption spectrum of the amine template-free porous materials
obtained in Examples 1-5. As a result, since all of the amine
template-free porous materials obtained in Examples 1-5 exhibited
absorption at 980 cm.sup.-1 based on Ti--O--P stretching vibration,
it was demonstrated that the amine template-free porous materials
obtained in Examples 1-5 had basic frameworks with titanium atoms
and phosphorus atoms bonded by way of oxygen atoms. FIG. 12 shows
the infrared absorption spectrum for the amine template-free porous
material obtained in Example 2. In the infrared absorption spectrum
shown in FIG. 12, in addition to the absorption at 980 cm.sup.-1
based on Ti--O--P stretching vibration there also appear absorption
near 3340 cm.sup.-1 based on --OH stretching vibration and
absorption near 1640 cm.sup.-1 based on the presence of water.
The infrared absorption spectra of the template-containing porous
materials or template-free porous materials obtained in Examples
6-13 were also measured in the same manner as described above. As a
result, since absorption near 980 cm.sup.-1 based on Ti--O--P
stretching vibration was observed in all of the porous materials
obtained in Examples 6-13, it was demonstrated that the porous
materials obtained in Examples 6-13 had basic frameworks with
titanium atoms and phosphorus atoms bonded by way of oxygen
atoms.
FIG. 13 shows the infrared absorption spectrum for the
template-containing porous material obtained in Example 6. The
absorption at 3340 cm.sup.-1, 2930 cm.sup.-1 and 2850 cm.sup.-1 is
believed to correspond to --O--H bonds in the basic framework of
the porous material, and the absorption at 1640 cm.sup.-1 is
believed to correspond to --C--H bonds of the template.
FIGS. 14 and 15 show, respectively, the infrared absorption
spectrum for the template-containing porous material obtained in
Example 10 and the infrared absorption spectrum for the
template-free porous material obtained in Example 10. Since the
absorption at 1175 cm.sup.-1, 1125 cm.sup.-1, 1035 cm.sup.-1 and
1005 cm.sup.-1 in FIG. 14 is not seen in FIG. 15, it was concluded
that these absorption peaks are based on the --SO.sub.3 H groups of
dodecyl-p-benzenesulfonic acid, and that the
dodecyl-p-benzenesulfonic acid was eliminated by treatment with the
mixed solution of ammonia water and ethanol.
The absorption near 3000 cm.sup.-1 in FIGS. 14 and 15 is attributed
to OH. Although absorption at 3150 cm.sup.-1 and 3400 cm.sup.-1 is
seen in FIG. 15 which shows the infrared absorption for the
template-removed porous materials, these are believed to be due to
free OH.sup.- and to OH groups, respectively. The absorption due to
free OH.sup.- disappears upon ion exchange with Cl.sup.- ion, and
reappears upon ion exchange with ammonia water.
In addition, the FT-IR spectra of the template-containing porous
material and template-removed porous material obtained in Example
14 were also measured in the manner described above. FIG. 16 shows
the FT-IR spectrum for the template-containing porous material
obtained in Example 14. In FIG. 16, the absorption at 3420
cm.sup.-1 is due to O--H stretching vibration in P--OH, the
absorption at 1630 cm.sup.-1 is due to deformation vibration of
adsorbed water, and the absorption at 1120-1020 cm.sup.-1 and 525
cm.sup.-1 is due to vibration of the P--O--Zr framework. The
absorption at 3200-3040 cm.sup.-1 seen in FIG. 16 is due to C--H
stretching vibration, the absorption at 2920-2850 cm.sup.-1 is due
to N--H stretching vibration and the absorption at 1510-1390
cm.sup.1 is due to N--H deformation vibration; however, these
absorptions were not seen in the spectrum for the template-removed
porous material.
.sup.31 P MAS NMR Spectroscopy
An MSL-300WB (Bruker Co.) was used to measure the .sup.33 P MAS NMR
spectra (.sup.31 P-NMR spectra by the magic angle rotation method)
for the amine template-containing porous materials obtained in
Examples 1 and 3-5 and the amine template-free porous material
obtained in Example 2. As a result, since signals near -26 ppm
based on P(OTi).sub.4 were observed in all of the porous materials
obtained in Examples 1 to 5, it was demonstrated that the porous
materials obtained in Examples 1 to 5 had basic frameworks with
titanium atoms and phosphorus atoms bonded by way of oxygen
atoms.
FIG. 17 shows a .sup.31 P MAS NMR spectrum for the amine
template-containing porous material obtained in Example 4, and FIG.
18 shows a .sup.31 P MAS NMR spectrum for the amine
template-containing porous material obtained in Example 5. The
signal near -25.2 ppm in FIG. 17 is attributed to P(OTi).sub.4, and
the signal near -11.6 ppm, the signal near -7.5 ppm and the signal
near 0 ppm are attributed to P(OH).sub.2 (OTi).sub.2, P(OH).sub.3
(OTi) and unreacted H.sub.3 PO.sub.4, respectively. The signal near
-25.8 ppm in FIG. 18 is attributed to P(OTi).sub.4, and the signal
near -19.9 ppm and the signal near 7.2 ppm are attributed to
P(OH)(OTi).sub.3 and P(OH).sub.3 (OTi), respectively.
The .sup.31 P MAS NMR spectra (.sup.31 P-NMR spectra by the magic
angle rotation method) for the template-containing porous materials
obtained in Examples 6 to 13 were measured in the same manner as
described above. As a result, since signals near -25 ppm based on
P(OTi).sub.4 were observed in all of the template-containing porous
materials obtained in Examples 6 to 13, it was demonstrated that
the porous materials obtained in Examples 6 to 13 had basic
frameworks with titanium atoms and phosphorus atoms bonded by way
of oxygen atoms.
FIG. 19 shows a .sup.31 P MAS NMR spectrum for the
template-containing porous material obtained in Example 6. The
signal near -26.0 ppm in FIG. 19 is attributed to P(OTi).sub.4,
while the signal near -20.0 ppm, the signal near -9.3 ppm and the
signal near -5.2 ppm are attributed to P(OH) (OTi).sub.3,
P(OH).sub.2 (OTi).sub.2 and P(OH).sub.3 (OTi), respectively. The
signal near 0.123 ppm is attributed to unreacted H.sub.3
PO.sub.4.
FIGS. 20 and 21 show the .sup.31 P MAS NMR spectra for the
template-containing porous materials obtained in Examples 7 and 9,
respectively. The signal near 7.2 ppm in FIG. 20 is attributed to
phosphonium cation (P.sup.+ (OTi).sub.4). The signal near 40 ppm in
FIG. 21 is attributed to CH.sub.3 P(OTi).sub.3.
The .sup.31 P MAS NMR spectra of the template-containing porous
material and template-removed porous material obtained in Example
14 were measured using the same measuring instruments mentioned
above, with phosphoric acid (H.sub.3 PO.sub.4) as the standard
sample. The results are shown in FIG. 22. Signals based on
P(OZr).sub.4 were also detected near -30 to -5 ppm in both of the
spectra in FIG. 22, thus confirming that these porous materials had
basic frameworks with zirconium atoms and phosphorus atoms bonded
by way of oxygen atoms. In the spectrum for the template-containing
porous material shown in FIG. 22, the signal near -7.0 ppm, the
signal near -10.8 ppm and the signal near -16.5 ppm are due to
phosphorus atoms with 4-coordinated structures. In the spectrum for
the template-removed porous material, there can be seen a chemical
shift from near -10.8 ppm to near -12.6 ppm and a chemical shift
from near -16.5 ppm to near -20.0 ppm, while no signal near -7.0
ppm is found. These chemical shifts and signal disappearance are
attributed to protonation from P--O.sup.- NR.sub.4.sup.+ to
P--O.sup.- H.sup.+ by removal of the template.
Nitrogen Adsorption
The amine template-tree porous materials obtained in Examples 1 to
5 were cooled to liquid nitrogen temperature (-196.degree. C.),
nitrogen gas was introduced, and the adsorption was determined by
the volume method. The pressure of the introduced nitrogen gas was
then gradually increased and the adsorption of nitrogen gas at each
equilibrium pressure was plotted to obtain a nitrogen adsorption
isotherm. When the BET specific surface area was determined from
this adsorption isotherm, the values of the BET specific surface
areas of the amine template-free porous materials of Examples 1 to
5 were small (for example, 132 m.sup.2 g.sup.-1 for the amine
template-free porous material obtained in Example 2), and the pore
sizes were believed to be close to the diameter of nitrogen
(micropores smaller than 1.5 nm diameter).
Next, the adsorption, nitrogen adsorption isotherm, pore size
distribution curve and median pore size were determined for
Examples 6 to 13 in the manner described above. As a result, all of
the median pore sizes of the template-free porous materials
obtained in Examples 6 to 13 were within the range of 1.5-30 nm.
For all of the template-free porous materials obtained in Examples
5 to 13, the value of the total volume of pores with a diameter in
the range of .+-.40% of the median pore diameter divided by the
total pore volume was within the range of 0.4-1.
The adsorption isotherms of the template-free porous materials
obtained in Examples 7, 8 and 9 are shown in FIGS. 23, 24 and 25,
respectively. FIG. 26 shows both the adsorption isotherm for the
template-free porous material obtained in Example 9 (the adsorption
isotherm indicated by "b" in FIG. 26) and the adsorption isotherm
for the template-free porous material obtained in Example 12 (the
adsorption isotherm indicated by "a" in FIG. 26). FIG. 26 also
shows the pore size distribution curves obtained by the BJH method
using these adsorption isotherms (a and b defined as above). From
FIG. 26 it is seen that the template-free porous material obtained
in Example 9 has a median pore size of 22.5 Angstroms (2.25 nm),
while the template-free porous material obtained in Example 12 has
a median pore size of 39 Angstroms (3.9 nm).
When the BET specific surface areas were determined from the
adsorption isotherms using a BET isotherm adsorption system, the
BET specific surface areas for Examples 7, 8, 9, 10, 12 and 13 were
found to be 687 m.sup.2 g.sup.-1, 615 m.sup.2 g.sup.-1, 727 m.sup.2
g.sup.-1, 512 m.sup.2 g.sup.-1, 464 m.sup.2 g.sup.-1 and 567
m.sup.2 g.sup.-1, respectively.
Next, the adsorption isotherm, pore size distribution curves and
median pore sizes for the template-removed porous material obtained
in Example 14 were determined in the same manner described above.
The SF method (Saito-Foley method) was used to determine the pore
size distribution curves. The obtained adsorption isotherms are
shown in FIG. 27 and the pore size distribution curves in FIG. 28.
The adsorption isotherms shown in FIG. 27 demonstrate that the
obtained porous material was mesoporous, with a BET specific
surface area of 275 m.sup.2 /g. The value of the BET specific
surface area is larger compared to the conventionally publicly
known laminar zirconium phosphate (BET specific surface area:
approximately 10-50 m.sup.2 /g). The median pore size of the porous
material was 1.1 nm.
Moisture Adsorption
The amine template-containing porous materials obtained in Examples
1 to 5 were immersed in water at 25.degree. C. and the adsorption
was measured by the volume method. Next, the pressure of the
adsorption water was gradually increased and the adsorption of the
water was plotted at each equilibrium pressure, to obtain a water
adsorption isotherm at 25.degree. C. As a result, since all of the
adsorption isotherms for Examples 1 to 5 exhibited Type I isotherms
with sudden spikes at a relative pressure of 0.1 or below, it was
demonstrated that the amine template-free porous materials obtained
in Examples 1 to 5 all had median pore sizes of from 0.2 nm to less
than 1.5 nm, indicating that the pores were in the micropore range.
When the pore volumes for the amine template-free porous materials
obtained in Examples 2 and 4 were determined from the adsorption
isotherms, the pore volumes were both found to be 0.12 ml/g.
FIG. 29 shows the moisture adsorption isotherm for the amine
template-free porous material obtained in Example 2, and FIG. 30
shows the moisture adsorption isotherm for the amine template-free
porous material obtained in Example 4, When the BET specific
surface areas were determined from the adsorption isotherms shown
in FIG. 29 and FIG. 30, the value of the BET specific surface area
of the amine template-free porous material obtained in Example 2
was found to be 425 m.sup.2 g.sup.-1, while the value of the BET
specific surface area of the amine template-free porous material
obtained in Example 4 was found to be 360 m.sup.2 g.sup.-1. These
values are larger than the values obtained with adsorption
isotherms by nitrogen adsorption. The moisture adsorption into the
amine template-free porous materials obtained in Examples 2 and 4
was found to comply with a Langmuir plot.
ICP Emission Spectroscopy
ICP (Inductively Coupled Plasma) emission spectroscopy of the amine
template-free porous materials obtained in Examples 1 to 5 was
conducted using an ICPS-2000 high-frequency plasma emission
spectroscope. As a result, the Ti/P molar ratios for the amine
template-free porous materials obtained in Examples 1 to 5 were
found to be 0.93, 0.96, 1.03, 0.95 and 0.98, respectively.
The compositional ratios of the basic frameworks for the amine
template-free porous materials obtained in Examples 1 to 5 wherein
titanium atoms and phosphorus atoms were bonded by way of oxygen
atoms were thus found to be Ti.sub.0.93 P.sub.1 O.sub.3-6,
Ti.sub.0.96 P.sub.1 O.sub.3-6, Ti.sub.1.03 P.sub.1 O.sub.3-6,
Ti.sub.0.95 P.sub.1 O.sub.3-6 and Ti.sub.0.98 P.sub.1 O.sub.3-6,
respectively.
The template-free porous materials obtained in Examples 6 to 13
were also subjected to ICP emission spectroscopy in the same manner
as above. As a result, The Ti/P molar ratios for the amine
template-free porous materials obtained in Examples 6-13 were found
to be 0.96, 1.05, 4.80, 1.02, 1.02, 3.8, 6.9 and 1.01,
respectively.
Thus, the compositional ratios of the basic frameworks for the
amine template-free porous materials obtained in Examples 6 to 13
wherein titanium atoms and phosphorus atoms were bonded by way of
oxygen atoms were found to be Ti.sub.1 P.sub.1.04 O.sub.2-5,
Ti.sub.1 P.sub.0.95 O.sub.2-5, Ti.sub.1 P.sub.0.21 O.sub.2-5,
Ti.sub.1 P.sub.0.98 O.sub.2-5, Ti.sub.1 P.sub.0.98 O.sub.2-5,
Ti.sub.1 P.sub.0.26 O.sub.2-5, Ti.sub.1 P.sub.0.14 O.sub.2-5 and
Ti.sub.1 P.sub.0.99 O.sub.2-5 respectively.
The Ti/P molar ratios for Examples 7-10, 12 and 13 are shown in
Table 1 below, together with the template types, autoclave heating
times, autoclave heating temperatures and BET specific surface
areas. For reference, Table 1 also shows results for a sample of
DTP (Disordered Titanium Phosphate) with a non-regular pore
arrangement structure.
TABLE 1 Autoclave Autoclave BET Ti/P heating heating surface
Template molar time temperature area Example No. type ratio (days)
(K) (m.sup.2 g.sup.-1) Example 7 SDS 1.05 3 333 687 Example 8 SDS
4.80 3 333 615 Example 9 SDS 1.02 2 318 727 Example 10 DBSA 1.02 1
318 512 Example 12 DBSA 6.9 1 318 464 Example 13 DBSA 1.10 1 318
567 Reference ODTMACl 0.98 1 298 380 Example SDS: Sodium dodecyl
sulfate DBSA: Dodecyl-p-benzenesulfonic acid ODTMAC1:
Octadecyltrimethylammonium chloride
Scanning Electron Microscope Observation
The amine template-containing porous materials obtained in Examples
1 and 4 were subjected to scanning electron microscope (SEM)
observation using a JSM-890 (product of JEOL Co.). The scanning
electron microscope photographs of the amine template-containing
porous materials obtained in Examples 1 and 4 are shown in FIG. 31
and FIG. 32. In FIG. 31, a granular porous material with a particle
size of a few hundred nm is seen, and in FIG. 32, a needle-like
porous material with a long axis of a few hundred nm is seen.
Scanning electron microscope (SEM) photographs were also obtained
for the template-containing porous material obtained in Example X,
in the same manner as above (FIGS. 33 and 34). FIG. 33 is
photographed at 50,000.times.magnification, and FIG. 34 at
25,000.times.magnification. FIGS. 33 and 34 both show the
template-containing porous material obtained in Example 6
aggregated to particle sizes of just under 1 .mu.m. FIG. 35 shows a
scanning electron microscope (SEM) photograph of the
template-containing porous material obtained in Example 13. FIG. 35
shows particles with a size of 20-60 nm aggregated to a size of
0.1-0.2 .mu.m.
A scanning electron microscope (SEM) photograph of the
template-containing porous material obtained in Example 14 was also
taken in the same manner as above (FIG. 36). The photograph shown
in FIG. 36 was taken at 20,000.times. magnification. FIG. 35 shows
globular crystals with a size of 0.2-0.3 .mu.m composed of
aggregates of fine particles sized 40-60 nm, such as seen in
microporous materials.
Transmission Electron Microscope Observation
FIGS. 37 and 38 show transmission electron microscope (TEM)
photographs of the template-containing porous materials obtained in
Examples 6 and 9. From the transmission electron microscope
photographs of FIGS. 37 and 38 it is seen that the
template-containing porous materials obtained in Examples 6 and 9
are mesoporous, with a 2-dimensional hexagonal pore arrangement
structure.
.sup.13 C MAS NMR Spectroscopy
An MSL-300WB (product of Bruker Co.) was used to measure the
.sup.13 C MAS NMR spectrum (.sup.13 C-NMR spectrum by the magic
angle rotation method) for the amine template-containing porous
material obtained in Example 5. The obtained .sup.13 C MAS NMR
spectrum is shown in FIG. 39. In FIG. 39 there are seen peaks at
42.3 ppm, 33.9 ppm, 29.5 ppm and 27.0 ppm due to
1,12-diaminododecane. The slight shift of the peak positions toward
the low chemical shift end is attributed to protonation to
1,12-diaminododecane during synthesis.
Ultraviolet/visible Light Absorption Spectroscopy
A 330 spectrophotometer (product of Hitachi Corp.) was used to
measure the ultraviolet/visible light absorption spectrum of the
amine template-free porous material obtained in Example 2. The
resulting spectrum is shown in FIG. 40. Since the amine
template-free porous material obtained in example 2 exhibits
absorption at 280-295 nm as shown in FIG. 40, this indicates that
the titanium atoms have a tetrahedral configuration, i.e. a
4-coordinated structure with four oxygen atoms positionable at the
four apices of the tetrahedron around each titanium atom, The
absorption in this region corresponds to transition from Ti.sup.4+
--O.sup.2- to Ti.sup.3+ --O.sup.-, thus indicating that the amine
template-free porous material obtained in Example 2 can function as
a photocatalyst by irradiation of light including this
wavelength.
The ultraviolet/visible light absorption spectra of the amine
template-free porous materials obtained in Examples 6 and 7 were
also measured in the sate manner as above. The spectra obtained for
Examples 6 and 7 are shown in FIGS. 41 and 42, respectively. Since
the template-free porous materials obtained in Examples 6 and 7
exhibit absorption at 280-295 nm, as shown in FIGS. 41 and 42, this
indicates that the titanium atoms have a tetrahedral configuration,
i.e. a 4-coordinated structure with four oxygen atoms positionable
at the four apices of the tetrahedron around each titanium atom.
The absorption in this region corresponds to transition from
Ti.sup.4+ --O.sup.2- to Ti.sup.3+ --O.sup.-, thus indicating that
the amine template-free porous materials obtained in Examples 6 and
7 can function as photocatalysts by irradiation of light including
this wavelength.
Ion-exchange Capacity Measurement
A 1 g portion of the amine template-free porous material obtained
in Example 2 was added to an aqueous solution of 1.75 g of
potassium chloride in 50 mL of water, and the mixture was stirred
to obtain a slurry. After refluxing the slurry for 4 hours at
80.degree. C. (353K), it was filtered and the obtained solid was
washed several times with water and dried at room temperature. The
dried solid was added to a solution of 1.0 g of ammonia water (25%
aqueous solution) diluted with 50 mL of water to make a slurry, and
this was refluxed at 80.degree. C. (353K) for 4 hours. After
completion of reflux, the slurry was filtered and the obtained
solid was washed with water. The chlorine content of the filtrate
was determined by potentiometric titration using a silver nitrate
(AgNO.sub.3) solution. The results indicated that the amine
template-free porous material obtained in Example 2 had an anion
exchange capacity of 4.71 mmol/g.
When the ion-exchange capacities of the template-free porous
materials obtained in Examples 10, 11 and 12 were determined in the
same manner as above, their anion exchange capacities were found to
be 5.39 mmol/g, 2.30 mmol/g and 1.43 mmol/g, respectively.
Presumed Reaction Mechanism for Examples 1-13
The results of the ultraviolet/visible absorption spectra for
Examples 1 to 13 indicated that the titanium atoms have a
tetrahedral configuration, i.e. that a 4-coordinated structure is
adopted with four oxygen atoms positionable at the four apices of
the tetrahedron around each titanium atom. Moreover, the results of
the infrared absorption spectroscopy clearly indicated Ti--O--P
bonding, while the results of the .sup.31 P MAS NMR spectroscopy
clearly indicated P(OTi).sub.4 bonding. The results of ICP emission
spectroscopy demonstrated that the molar ratio of Ti and P was
roughly 1:1. It was also indicated that the porous materials
obtained in the examples have an anion exchange property. The
porous materials also exhibit a cationic exchange property. By
summarizing these results, it is theorized that the reactions of
Examples 1 to 13 proceed by the reaction pathway illustrated in
FIG. 43.
Specifically, reaction between one molecule of titanium
tetrachloride (TiCl.sub.4) and one molecule of phosphoric acid
(H.sub.3 PO.sub.4) results in elimination of HCl, yielding a
compound with the structure represented by (a). This compound
further reacts with titanium tetrachloride and phosphoric acid
resulting in elimination of HCl and yielding a compound with the
structure represented by (b). Since the --OH and .dbd.O bonded to
the phosphorus atoms at one end of the compound with the structure
represented by (b) can further react with titanium tetrachloride
while the --Cl bonded to the titanium atom at the other end can
further react with phosphoric acid, these reactions take place
simultaneously by the reaction pathway represented by (II), and
both ends of the compound with the structure represented by (b)
extend to yield a compound with the structure represented by (d),
wherein the phosphorus atoms and titanium atoms are bonded by way
of oxygen atoms.
The compound represented by (d) comprises titanium atoms with a
4-coordinated structure (with oxygen atoms positioned at the four
apices of the tetrahedron around each titanium atom) and phosphorus
atoms with a 4-coordinated structure (with oxygen atoms positioned
at the four apices of the tetrahedron around each phosphorus atom),
and therefore the phosphorus atoms are positively charged.
Consequently, as shown in FIG. 43, the positively charged
phosphorus atoms form ion pairs with negative ions represented by
X.sup.- (for example, OH.sup.-), and the X.sup.- ions are
ion-exchanged with other anions. It is believed that the porous
materials of the invention exhibit an anion-exchange property
because of the positively charged phosphorus atoms in the
molecule.
On the other hand, in the compound with the structure represented
by (b), when the --Cl bonded to a titanium atom participates in
further reaction with the phosphoric acid by the reaction pathway
represented by (I), a compound with the structure represented by
(c) is produced. In the structure represented by (c), the
phosphorus atoms are bonded with one double-bonding oxygen and
three single-bonding oxygens, and therefore the molecule is neutral
as a whole. However, the --OH group bonded to the phosphorus atom
tends to polarize to --O.sup.- --H.sup.+, and this H.sup.+ is
ion-exchanged with other cations. It is believed that the porous
materials of the invention exhibit a cation-exchange property
because of the presence of the --O.sup.- --H.sup.+ groups in the
molecule.
In Examples 9 and 13, as indicated by the results of .sup.31 P MAS
NMR spectroscopy, methylphosphonic acid diethyl ester (CH.sub.3
PO(OC.sub.2 H.sub.5).sub.2) is also incorporated into the
above-mentioned reactions, and therefore phosphorus atoms with
bonded methyl groups are also bonded to titanium atoms by way of
oxygen atoms. Consequently, when an alkylphosphonic acid ester such
as methylphosphonic acid diethyl ester is used in addition to
phosphoric acid, a basic framework is formed which includes
alkyl-bonded phosphorus atoms, thus allowing modification with
alkyl groups. A similar reaction occurs even when an
alkylphosphonic acid is used instead of an alkylphosphonic acid
ester, forming a basic framework including alkyl-bonded phosphorus
atoms.
Presumed Reaction Mechanism for Example 14
Based on the above results, it is theorized that the porous
material obtained in Example 14 forms its basic framework by the
reaction pathway illustrated in FIG. 44.
Specifically, the two amino groups of 1,12-diaminododecane are
protonated in the presence of phosphoric acid to --NH.sub.3.sup.+,
and aggregation occurs with the hydrophobic portions oriented
toward the center and the hydrophilic portions oriented outward,
while the --NH.sub.3.sup.+ charges on the outside are balanced by
the phosphoric acid ions (PO.sub.4.sup.3-), thereby forming
globules. When zirconium tetrapropoxide is added to these globules,
the zirconium is rapidly oriented near the phosphoric acid ions of
the globules, and P--O--Zr is formed upon hydrothermal treatment to
produce a template-containing porous material (left side of FIG.
44).
When the template-containing porous material produced in this
manner is treated with a hydrochloric acid/ethanol solution, the
oxygen atoms (--O.sup.-) bonded to the --NH.sub.3.sup.+ are
protonated with elimination of the 1,2-diaminododecane, thus
yielding the target porous material (right side of FIG. 44). This
reaction mechanism is also suggested by the fact that the pore size
of the porous material after template removal closely matches the
molecular length of 1,2-diaminododecane.
Decomposition of Water by Light Irradiation
Example 15
A 1 g portion of the amine template-free porous material obtained
in Example 3 was dispersed in 150 ml of water held in a quartz
photoreactor. To this there was added 4 g of sodium bicarbonate,
and the mixture was stirred under reduced pressure. Argon gas was
then introduced to 100 Torr, and ultraviolet/visible light
irradiation was performed with a xenon lamp. The gas composition
was analyzed at 4, 6, 8, 10, 12, 16, 20 and 24 hours after
initiating the ultraviolet/visible light irradiation. A TCD
(thermal conductivity detector)-equipped GC-8APT gas chromatograph
(product of Shimadzu Seisakusho) was used for the gas composition
analysis. A hydrogen gas calibration curve was used to determine
the hydrogen gas volume generated by the aforementioned
photocatalytic reaction. The results are shown in FIG. 45. As
clearly seen in FIG. 45, the porous material obtained in Example 3
(amine template-free porous material) was able to decompose water
into hydrogen gas and oxygen gas by photocatalytic reaction, and
the decomposition reaction was efficiently produced.
Example 16
Photodecomposition of water was carried out by the procedure
described below using the template-removed porous material obtained
in Example 14 as the catalyst, and the catalytic activity was
evaluated.
The photodecomposition of water was accomplished using a gas phase
circulating reactor. The reactor was equipped with a quartz
reaction vessel with in an inner volume of 400 ml, and evacuation
of the inside of the reaction vessel was accomplished with a vacuum
pump, The gas phase circulation channel of the reactor was
connected to an online gas chromatograph (detector: TCD, FID), to
allow analysis of the gas composition after prescribed periods of
time.
Using this type of reactor, an aqueous solution of 5.3 g of sodium
sulfite (Na.sub.2 SO.sub.3) dissolved in 175 ml of water was placed
in the reaction vessel together with 1 g of the template-removed
porous material, and the vessel was placed in the reactor. After
then evacuating the gas in the reaction vessel and the gas phase
circulation channel, argon gas was introduced to 60 Torr and the
mixture in the reaction vessel was irradiated with a xenon (Xe)
lamp (output: 300 W) while stirring with a magnetic stirrer. After
a prescribed period of time had passed, the amount of hydrogen
produced by the reaction was measured with the gas
chromatograph.
In this reaction, the hydrogen generation upon one hour of light
irradiation was 3.9 mmol per gram of catalyst. FIG. 46 shows the
correlation between reaction time and hydrogen generation after 3
repeated cycles, where one cycle was a period from the initial
light irradiation to 24 hours thereafter. The hydrogen generation
amounts in cycles 1 to 3 were 84.2 mmol, 32.7 mmol and 81.8 mmol,
respectively, per gram of catalyst, thus confirming that the porous
material used exhibits sufficiently high catalytic activity over
long periods. No oxygen was detected in this reaction.
Comparative Example 1
Water was subjected to photodecomposition in the same manner as
Example 16 except that a template-removed porous material was not
used. The hydrogen generation upon 24 hours of light irradiation
was 10.7 mmol.
Comparative Example 2
Water was subjected to photodecomposition in the same manner as
Example 16 except that platinum-carrying titanium (Pt/TiO.sub.2)
was used instead of a template-removed porous material, and sodium
carbonate (Na.sub.2 CO.sub.3) was used instead of sodium sulfite.
The hydrogen generation upon 1 hour of light irradiation was 0.57
mmol per gram of catalyst.
Comparative Example 3
Water was subjected to photodecomposition in the same manner as
Example 16 except that zirconia (ZrO.sub.2) was used instead of a
template-removed porous material, and sodium bicarbonate
(NaHCO.sub.3) was used instead of sodium sulfite. The hydrogen
generation upon 1 hour of light irradiation was 0.31 mmol per gram
of catalyst.
As explained above, according to the present invention there can be
provided photocatalysts capable of efficiently producing
photocatalytic reaction even with low amounts of catalyst and a
small light irradiation areas to allow decomposition of water and
the like with an adequately high reaction rate, as well as a
production process for the photocatalysts.
From the invention thus described, it will be obvious that the
embodiments of the invention may be varied in many ways. Such
variations are not to be regarded as a departure from the spirit
and scope of the invention, and all such modifications as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
* * * * *